an extensive and exact knowledge of the vegetable world, and what
comprehensive views of affinity, must be requisite in a person who
has to modify the natural system so as to make it suited to receive
and arrange a great number of new plants, extremely different from
the genera on which the arrangement was first formed, as the New
Holland genera for the most part were. He will also see how
impossible it must be to convey by extract or description any notion
of the nature of these modifications: it is enough to say, that they
have excited the applause of botanists wherever the science is
studied, and that they have induced M. de Humboldt and his
fellow-laborers, themselves botanists of the first rank, to dedicate
one of their works to him in terms of the strongest
admiration.[123\16] Mr. Brown has also published {410} special
disquisitions on parts of the Natural System; as on Jussieu's
_Proteaceæ_;[124\16] on the _Asclepiadeæ_, a natural family of
plants which must be separated from Jussieu's _Apocyneæ_;[125\16]
and other similar labors.
[Note 123\16: Roberto Brown, Britanniarum gloriæ atque ornamento,
totam Botanices scientiam ingenio mirifico complectenti. &c.]
[Note 124\16: _Linn. Tr._ vol. x. 1809.]
[Note 125\16: _Mem. of Wernerian N. H. Soc._ vol. i. 1809.]
We have, I think, been led, by our survey of the history of Botany,
to this point;--that a Natural Method directs us to the study of
Physiology, as the only means by which we can reach the object. This
conviction, which in botany comes at the end of a long series of
attempts at classification, offers itself at once in the natural
history of animals, where the physiological signification of the
resemblances and differences is so much more obvious. I shall not,
therefore, consider any of these branches of natural history in
detail as examples of mere classification. They will come before us,
if at all, more properly when we consider the classifications which
depend on the functions of organs, and on the corresponding
modifications which they necessarily undergo; that is, when we trace
the results of Physiology. But before we proceed to sketch the
history of that part of our knowledge, there are a few points in the
progress of Zoology, understood as a mere classificatory science,
which appear to me sufficiently instructive to make it worth our
while to dwell upon them.
[2nd Ed.] [Mr. Lindley's recent work, _The Vegetable Kingdom_ (1846),
may be looked upon as containing the best view of the recent history
of Systematic Botany. In the Introduction to this work, Mr. Lindley
has given an account of various recent works on the subject; as
Agardh's _Classes Plantarum_ (1826); Perleb's _Lehrbuch der
Naturgeschichte der Pflanzenreich_ (1826); Dumortier's _Florula
Belgica_ (1827); Bartling's _Ordines Naturales Plantarum_ (1830);
Hess's _Uebersicht der Phanerogenischen Natürlichen Pflanzenfamilien_
(1832); Schulz's _Natürliches System des Pflanzenreich's_ (1832);
Horaninow's _Primæ Lineæ Systematis Naturæ_ (1834); Fries's _Corpus
Florarum provincialium Sueciæ_ (1835); Martins's _Conspectus Regni
Vegetablis secundum Characteres Morphologicos_ (1835); Sir Edward F.
Bromhead's System, as published in the _Edinburgh Journal_ and other
Journals (1836-1840); Endlicher's _Genera Plantarum secundum Ordines
Naturales disposita_ (1836-1840); Perleb's _Clavis Classicum Ordinum
et Familiarum_ (1838); Adolphe Brongniart's _Enumération des Genres de
Plantes_ (1843); Meisner's _Plantarum vascularium Genera secundum
Ordines Naturales digesta_ (1843); Horaninow's _Tetractys Naturæ, seu
Systema quinquemembre omnium Naturalium_ {411} (1843); Adrien de
Jussieu's _**Cours Elémentaire d'Histoire Naturelle. Botanique_
(1844).
Mr. Lindley, in this as in all his works, urges strongly the
superior value of natural as compared with artificial systems; his
principles being, I think, nearly such as I have attempted to
establish in the _Philosophy of the Sciences_, Book viii., Chapter
ii. He states that the leading idea which has been kept in view in
the compilation of his work is this maxim of Fries: "Singula sphæra
(sectio) _ideam quandam_ exponit, indeque ejus character notione
simplici optime exprimitur;" and he is hence led to think that the
true characters of all natural assemblages are extremely simple.
One of the leading features in Mr. Lindley's system is that he has
thrown the Natural Orders into groups subordinate to the higher
divisions of Classes and Sub-classes. He had already attempted this,
in imitation of Agardh and Bartling, in his _Nixus Plantarum_
(1838). The groups of Natural Orders were there called _Nixus_
(tendencies); and they were denoted by names ending in _ales_; but
these groups were further subordinated to _Cohorts_. Thus the first
member of the arrangement was Class 1. EXOGENÆ. Sub-class 1.
POLYPETALÆ. Cohort 1. ALBUMINOSÆ. _Nixus_ 1. _Ranales_. Natural
Orders included in this _Nixus_, Ranunculaceæ, Saraceniceæ,
Papaveraceæ, &c. In the _Vegetable Kingdom_, the groups of Natural
Orders are termed _Alliances_. In this work, the Sub-classes of the
EXOGENS are four: I. DICLINOUS; II. HYPOGYNOUS; III. PERIGYNOUS; IV.
EPIGYNOUS; and the Alliances are subordinated to these without the
intervention of _Cohorts_.
Mr. Lindley has also, in this as in other works, given English names
for the Natural Orders. Thus for _Nymphaceæ_, _Ranunculaceæ_,
_Tamaricaceæ_, _Zygophyllaceæ_, _Eleatrinaceæ_, he substitutes
Water-Lilies, Crowfoots, Tamarisks, Bean-Capers, and Water-Peppers;
for _Malvaceæ_, _Aurantiaceæ_, _Gentianaceæ_, _Primulaceæ_,
_Urtiaceæ_, _Euphorbiaceæ_, he employs Mallow-worts, Citron-worts,
Gentian-worts, Prim-worts, Nettle-worts, Spurge-worts; and the terms
Orchids, Hippurids, Amaryllids, Irids, Typhads, Arads, Cucurbits,
are taken as English equivalents for _Orchidaceæ_, _Haloragaceæ_,
_Amaryllidaceæ_, _Iridaceæ_, _Typhaceæ_, _Araceæ_, _Cucurbitaceæ_.
All persons who wish success to the study of botany in England must
rejoice to see it tend to assume this idiomatic shape.] {412}
CHAPTER VI.
THE PROGRESS OF SYSTEMATIC ZOOLOGY.
THE history of Systematic Botany, as we have presented it, may be
considered as a sufficient type of the general order of progression
in the sciences of classification. It has appeared, in the survey
which we have had to give, that this science, no less than those
which we first considered, has been formed by a series of inductive
processes, and has, in its history, Epochs at which, by such
processes, decided advances were made. The important step in such
cases is, the seizing upon some artificial mark which conforms to
natural resemblances;--some basis of arrangement and nomenclature by
means of which true propositions of considerable generality can be
enunciated. The advance of other classificatory sciences, as well as
botany, must consist of such steps; and their course, like that of
botany, must (if we attend only to the real additions made to
knowledge,) be gradual and progressive, from the earliest times to
the present.
To exemplify this continued and constant progression in the whole
range of Zoology, would require vast knowledge and great labor; and
is, perhaps, the less necessary, after we have dwelt so long on the
history of Botany, considered in the same point of view. But there
are a few observations respecting Zoology in general which we are
led to make in consequence of statements recently promulgated; for
these statements seem to represent the history of Zoology as having
followed a course very different from that which we have just
ascribed to the classificatory sciences in general. It is held by
some naturalists, that not only the formation of a systematic
classification in Zoology dates as far back as Aristotle; but that
his classification is, in many respects, superior to some of the
most admired and recent attempts of modern times.
If this were really the case, it would show that at least the idea
of a Systematic Classification had been formed and developed long
previous to the period to which we have assigned such a step; and it
would be difficult to reconcile such an early maturity of Zoology
with the conviction, which we have had impressed upon us by the
other {413} parts of our history, that not only labor but time, not
only one man of genius but several, and those succeeding each other,
are requisite to the formation of any considerable science.
But, in reality, the statements to which we refer, respecting the
scientific character of Aristotle's Zoological system, are
altogether without foundation; and this science confirms the lessons
taught us by all the others. The misstatements respecting
Aristotle's doctrines are on this account so important, and are so
curious in themselves, that I must dwell upon them a little.
Aristotle's nine Books _On Animals_ are a work enumerating the
differences of animals in almost all conceivable respects;--in the
organs of sense, of motion, of nutrition, the interior anatomy, the
exterior covering, the manner of life, growth, generation, and many
other circumstances. These differences are very philosophically
estimated. "The corresponding parts of animals," he says,[126\16]
"besides the differences of quality and circumstance, differ in
being more or fewer, greater or smaller, and, speaking generally, in
excess and defect. Thus some animals have crustaceous coverings,
others hard shells; some have long beaks, some short; some have many
wings, some have few; Some again have parts which others want, as
crests and spurs." He then makes the following important remark:
"Some animals have parts which correspond to those of others, not as
being the same in species, nor by excess and defect, but by
_analogy_; thus a claw is analogous to a thorn, and a nail to a
hoof, and a hand to the nipper of a lobster, and a feather to a
scale; for what a feather is in a bird, that is a scale in a fish."
[Note 126\16: Lib. i. c. i.]
It will not, however, be necessary, in order to understand Aristotle
for our present purpose, that we should discuss his notion of
Analogy. He proceeds to state his object,[127\16] which is, as we
have said, to describe the differences of animals in their structure
and habits. He then observes, that for structure, we may take Man
for our type,[128\16] as being best known to us; and the remainder
of the first Book is occupied with a description of man's body,
beginning from the head, and proceeding to the extremities.
[Note 127\16: Lib. i. c. ii.]
[Note 128\16: c. iii.]
In the next Book, (from which are taken the principal passages in
which his modern commentators detect his system,) he proceeds to
compare the differences of parts in different animals, according to
the order which he had observed in man. In the first chapter he
speaks {414} of the head and neck of animals; in the second, of the
parts analogous to arms and hands; in the third, of the breast and
paps, and so on; and thus he comes, in the seventh chapter, to the
legs, feet, and toes: and in the eleventh, to the teeth, and so to
other parts.
The construction of a classification consists in the selection of
certain parts, as those which shall eminently and peculiarly
determine the place of each species in our arrangement. It is clear,
therefore, that such an enumeration of differences as we have
described, supposing it complete, contains the materials of all
possible classifications. But we can with no more propriety say that
the author of such an enumeration of differences is the author of
any classification which can be made by means of them, than we can
say that a man who writes down the whole alphabet writes down the
solution of a given riddle or the answer to a particular question.
Yet it is on no other ground than this enumeration, so far as I can
discover, that Aristotle's "System" has been so decidedly spoken
of,[129\16] and exhibited in the most formal tabular shape. The
authors of this _Systema Aristotelicum_, have selected, I presume,
the following passages from the work _On Animals_, as they might
have selected any other; and by arranging them according to a
subordination unknown to Aristotle himself have made for him a
scheme which undoubtedly bears a great resemblance to the most
complete systems of modern times.
[Note 129\16: _Linnæan Transactions_, vol. xvi. p. 24.]
Book I., chap. v.--"Some animals are viviparous, some oviparous,
some vermiparous. The viviparous are such as man, and the horse, and
all those animals which have hair; and of aquatic animals, the whale
kind, as the dolphin and cartilaginous fishes."
Book II., chap. vii.--"Of quadrupeds which have blood and are
viviparous, some are (as to their extremities,) many-cloven, as the
hands and feet of man. For some are many-toed, as the lion, the dog,
the panther; some are bifid, and have hoofs instead of nails, as the
sheep, the goat, the elephant, the hippopotamus; and some have
undivided feet, as the solid-hoofed animals, the horse and ass. The
swine kind share both characters."
Chap. ii.--"Animals have also great differences in the teeth, both
when compared with each other and with man. For all quadrupeds which
have blood and are viviparous, have teeth. And in the first place,
some are ambidental,[130\16] (having teeth in both jaws;) and some
{415} are not so, wanting the front teeth in the upper jaw. Some
have neither front teeth nor horns, as the camel; some have
tusks,[131\16] as the boar, some have not. Some have
serrated[132\16] teeth, as the lion, the panther, the dog; some have
the teeth unvaried,[133\16] as the horse and the ox; for the animals
which vary their cutting-teeth have all serrated teeth. No animal
has both tusks and horns; nor has any animal with serrated teeth
either of those weapons. The greater part have the front teeth
cutting, and those within broad."
[Note 130\16: Ἀμφόδοντα.]
[Note 131\16: Χαυλιόδοντα.]
[Note 132\16: Καρχαρόδοντα.]
[Note 133\16: Ἀνεπάλλακτα.]
These passages undoubtedly contain most of the differences on which
the asserted Aristotelian classification rests; but the
classification is formed by using the characters drawn from the
teeth, in order to subdivide those taken from the feet; whereas in
Aristotle these two sets of characters stand side by side, along
with dozens of others; any selection of which, employed according to
any arbitrary method of subordination, might with equal justice be
called Aristotle's system.
Why, for instance, in order to form subdivisions of animals, should
we not go on with Aristotle's continuation of the second of the
above quoted passages, instead of capriciously leaping to the third?
"Of these some have horns, some have none . . . Some have a
fetlock-joint,[134\16] some have none . . . Of those which have
horns, some have them solid throughout, as the stag; others, for the
most part, hollow . . . Some cast their horns, some do not." If it
be replied, that we could not, by means of such characters, form a
tenable zoological system; we again ask by what right we assume
Aristotle to have made or attempted a systematic arrangement, when
what he has written, taken in its natural order, does not admit of
being construed into a system.
[Note 134\16: Ἀστράγαλον.]
Again, what is the object of any classification? This, at least,
among others. To enable the person who uses it to study and describe
more conveniently the objects thus classified. If, therefore,
Aristotle had formed or adopted any system of arrangement, we should
see it in the order of the subjects in his work. Accordingly, so far
as he has a system, he professes to make this use of it. At the
beginning of the fifth Book, where he is proceeding to treat of the
different modes of generation of animals, he says, "As we formerly
made a Division of animals according to their kinds, we must now, in
the same manner, give a general survey of their History (θεωρίαν).
Except, indeed, that in the former case we made our commencement by
a description {416} of man, but in the present instance we must
speak of him last, because he requires most study. We must begin
then with those animals which have shells; we must go on to those
which have softer coverings, as crustacea, soft animals, and
insects; after these, fishes, both viviparous and oviparous; then
birds; then land animals, both viviparous and oviparous."
It is clear from this passage that Aristotle had certain wide and
indefinite views of classification, which though not very exact, are
still highly creditable to him; but it is equally clear that he was
quite unconscious of the classification that has been ascribed to
him. If he had adopted that or any other system, this was precisely
the place in which he must have referred to and employed it.
The honor due to the stupendous accumulation of zoological knowledge
which Aristotle's works contain, cannot be tarnished by our denying
him the credit of a system which he never dreamt of and which, from
the nature of the progress of science, could not possibly be
constructed at that period. But, in reality, we may exchange the
mistaken claims which we have been contesting for a better, because
a truer praise. Aristotle does show, as far as could be done at his
time, a perception of the need of groups, and of names of groups, in
the study of the animal kingdom; and thus may justly be held up as
the great figure in the Prelude to the Formation of Systems which
took place in more advanced scientific times.
This appears, in some measure, from the passage last quoted. For not
only is there, in that, a clear recognition of the value and object
of a method in natural history; but the general arrangement of the
animal kingdom there proposed has considerable scientific merit, and
is, for the time, very philosophical. But there are passages in his
work in which he shows a wish to carry the principle of arrangement
more into detail. Thus, in the first Book, before proceeding to his
survey of the differences of animals,[135\16] after speaking of such
classes as Quadrupeds. Birds, Fishes, Cetaceous, Testaceous,
Crustaceous Animals, Mollusks, Insects, he says, (chap. vii.)
"Animals cannot be divided into large genera, in which one kind
includes many kinds. For some kinds are unique, and have no
difference of species, as _man_. Some have such kinds, but have no
names for them. Thus all quadrupeds which have not wings, have
blood. But of these, some are viviparous, some oviparous. Those
which are {417} viviparous have not all hair; those which are
oviparous have scales." We have here a manifestly intentional
subordination of characters: and a kind of regret that we have not
names for the classes here indicated; such, for instance, as
viviparous quadrupeds having hair. But he follows the subject into
further detail. "Of the class of viviparous quadrupeds," he
continues, "there are many genera,[136\16] but these again are
without names, except specific names, such as _man_, _lion_, _stag_,
_horse_, _dog_, and the like. Yet there is a genus of animals that
have names, as the horse, the ass, the _oreus_, the _ginnus_, the
_innus_, and the animal which in Syria is called _heminus_ (mule);
for these are called _mules_, from their resemblance only; not being
mules, for they breed of their own kind. Wherefore," he adds, that
is, because we do not possess recognized genera and generic names of
this kind, "we must take the species separately, and study the
nature of each."
[Note 135\16: Γένη.]
[Note 136\16: **Εἴδη.]
These passages afford us sufficient ground for placing Aristotle at
the head of those naturalists to whom the first views of the
necessity of a zoological system are due. It was, however, very long
before any worthy successor appeared, for no additional step was
made till modern times. When Natural History again came to be
studied in Nature, the business of Classification, as we have seen,
forced itself upon men's attention, and was pursued with interest in
animals, as in plants. The steps of its advance were similar in the
two cases;--by successive naturalists, various systems of artificial
marks were selected with a view to precision and convenience;--and
these artificial systems assumed the existence of certain natural
groups, and of a natural system to which they gradually tended. But
there was this difference between botany and zoology:--the reference
to physiological principles, which, as we have remarked, influenced
the natural systems of vegetables in a latent and obscure manner,
botanists being guided by its light, but hardly aware that they were
so, affected the study of systematic zoology more directly and
evidently. For men can neither overlook the general physiological
features of animals, nor avoid being swayed by them in their
judgments of the affinities of different species. Thus the
classifications of zoology tended more and more to a union with
comparative anatomy, as the science was more and more
improved.[137\16] But comparative anatomy belongs to the subject of
the next Book; and anything it may be proper to say respecting its
influence upon zoological arrangements, will properly find a place
there. {418}
[Note 137\16: Cuvier, _Leç. d'Anat. Comp._ vol. i. p. 17.]
It will appear, and indeed it hardly requires to be proved, that
those steps in systematic zoology which are due to the light thrown
upon the subject by physiology, are the result of a long series of
labors by various naturalists, and have been, like other advances in
science, led to and produced by the general progress of such
knowledge. We can hardly expect that the classificatory sciences can
undergo any material improvement which is not of this kind. Very
recently, however, some authors have attempted to introduce into
these sciences certain principles which do not, at first sight,
appear as a continuation and extension of the previous researches of
comparative anatomists. I speak, in particular, of the doctrines of
a _Circular Progression_ in the series of affinity; of a _Quinary
Division_ of such circular groups; and of a relation of _Analogy_
between the members of such groups, entirely distinct from the
relation of _Affinity_.
The doctrine of Circular Progression has been propounded principally
by Mr. Macleay; although, as he has shown,[138\16] there are
suggestions of the same kind to be found in other writers. So far as
this view negatives the doctrine of a mere linear progression in
nature, which would place each genus in contact only with the
preceding and succeeding ones, and so far as it requires us to
attend to more varied and ramified resemblances, there can be no
doubt that it is supported by the result of all the attempts to form
natural systems. But whether that assemblage of circles of
arrangement which is now offered to naturalists, be the true and
only way of exhibiting the natural relations of organized bodies, is
a much more difficult question, and one which I shall not here
attempt to examine; although it will be found, I think, that those
analogies of science which we have had to study, would not fail to
throw some light upon such an inquiry. The prevalence of an
invariable numerical law in the divisions of natural groups, (as the
number _five_ is asserted to prevail by Mr. Macleay, the number
_ten_ by Fries, and other numbers by other writers), would be a
curious fact, if established; but it is easy to see that nothing
short of the most consummate knowledge of natural history, joined
with extreme clearness of view and calmness of judgment, could
enable any one to pronounce on the attempts which have been made to
establish such a principle. But the doctrine of a relation of
_Analogy_ distinct from Affinity, in the manner which has recently
been taught, seems to be obviously at variance with that gradual
approximation of the classificatory to the {419} physiological
sciences, which has appeared to us to be the general tendency of
real knowledge. It seems difficult to understand how a reference to
such relations as those which are offered as examples of
analogy[139\16] can be otherwise than a retrograde step in science.
[Note 138\16: _Linn. Trans._ vol. xvi. p. 9.]
[Note 139\16: For example, the goatsucker has an _affinity_ with the
swallow; but it has an _analogy_ with the bat, because both fly at
the same hour of the day, and feed in the same manner.--Swainson,
_Geography and Classification of Animals_, p. 129.]
Without, however, now dwelling upon these points, I will treat a
little more in detail of one of the branches of Zoology.
[2nd Ed.] [For the more recent progress of Systematic Zoology, see
in the _Reports_ of the British Association, in 1834, Mr. L.
Jenyns's _Report an the Recent Progress and Present State of
Zoology_, and in 1844, Mr. Strickland's _Report on the Recent
Progress and Present State of Ornithology_. In these Reports, the
questions of the Circular Arrangement, the Quinary System, and the
relation of Analogy and Affinity are discussed.]
CHAPTER VII.
THE PROGRESS OF ICHTHYOLOGY.
IF it had been already observed and admitted that sciences of the
same kind follow, and must follow, the same course in the order of
their development, it would be unnecessary to give a history of any
special branch of Systematic Zoology; since botany has already
afforded us a sufficient example of the progress of the
classificatory sciences. But we may be excused for introducing a
sketch of the advance of one department of zoology, since we are led
to the attempt by the peculiar advantage we possess in having a
complete history of the subject written with great care, and brought
up to the present time, by a naturalist of unequalled talents and
knowledge. I speak of Cuvier's _Historical View of Ichthyology_,
which forms the first chapter of his great work on that part of
natural history. The place and office in the progress of this
science, which is assigned to each person by Cuvier, will probably
not be lightly contested. It will, therefore, be no small
confirmation of the justice of the views on which the {420}
distribution of the events in the history of botany was founded, if
Cuvier's representation of the history of ichthyology offers to us
obviously a distribution almost identical.
We shall find that this is so;--that we have, in zoology as in botany,
a period of unsystematic knowledge; a period of misapplied erudition;
an epoch of the discovery of fixed characters; a period in which many
systems were put forward; a struggle of an artificial and a natural
method; and a gradual tendency of the natural method to a manifestly
physiological character. A few references to Cuvier's history will
enable us to illustrate these and other analogies.
_Period of Unsystematic Knowledge._--It would be easy to collect a
number of the fabulous stories of early times, which formed a
portion of the imaginary knowledge of men concerning animals as well
as plants. But passing over these, we come to a long period and a
great collection of writers, who, in various ways, and with various
degrees of merit, contributed to augment the knowledge which existed
concerning fish, while as yet there was hardly ever any attempt at a
classification of that province of the animal kingdom. Among these
writers, Aristotle is by far the most important. Indeed he carried
on his zoological researches under advantages which rarely fall to
the lot of the naturalist; if it be true, as Athenæus and Pliny
state,[140\16] that Alexander gave him sums which amounted to nine
hundred talents, to enable him to collect materials for his history
of animals, and put at his disposal several thousands of men to be
employed in hunting, fishing, and procuring information for him. The
works of his on Natural History which remain to us are, nine Books
_Of the History of Animals_; four, _On the Parts of Animals_; five,
_On the Generation of Animals_; one, _On the Going of Animals_; one,
_Of the Sensations, and the Organs of them_; one, _On Sleeping and
Waking_; one, _On the Motion of Animals_; one, _On the Length and
Shortness of Life_; one, _On Youth and Old Age_; one, _On Life and
Death_; one, _On Respiration_. The knowledge of the external and
internal conformation of animals, their habits, instincts, and uses,
which Aristotle displays in these works, is spoken of as something
wonderful even to the naturalists of our own time. And he may be
taken as a sufficient representative of the whole of the period of
which we speak; for he is, says Cuvier,[141\16] not only the first,
but the only one of the ancients who has treated of the natural
history of fishes (the province to which {421} we now confine
ourselves,) in a scientific point of view, and in a way which shows
genius.
[Note 140\16: Cuv. _Hist. Nat. des Poissons_, i. 13.]
[Note 141\16: Cuv. p. 18.]
We may pass over, therefore, the other ancient authors from whose
writings Cuvier, with great learning and sagacity, has levied
contributions to the history of ichthyology; as Theophrastus, Ovid,
Pliny, Oppian, Athenæus, Ælian, Ausonius, Galen. We may, too, leave
unnoticed the compilers of the middle ages, who did little but
abstract and disfigure the portions of natural history which they
found in the ancients. Ichthyological, like other knowledge, was
scarcely sought except in books, and on that very account was not
understood when it was found.
_Period of Erudition._--Better times at length came, and men began to
observe nature for themselves. The three great authors who are held to
be the founders of modern ichthyology, appeared in the middle of the
sixteenth century; these were Bélon, Rondelet, and Salviani, who all
published about 1555. All the three, very different from the compilers
who filled the interval from Aristotle to them, themselves saw and
examined the fishes which they describe, and have given faithful
representations of them. But, resembling in that respect the founders
of modern botany, Briassavola, Ruellius, Tragus, and others, they
resembled them in this also, that they attempted to make their own
observations a commentary upon the ancient writers. Faithful to the
spirit of their time, they are far more careful to make out the names
which each fish bore in the ancient world, and to bring together
scraps of their history from the authors in whom these names occur,
than to describe them in a lucid manner; so that without their
figures, says Cuvier, it would be almost as difficult to discover
their species as those of the ancients.
The difficulty of describing and naming species so that they can be
recognized, is little appreciated at first, although it is in
reality the main-spring of the progress of the sciences of
classification. Aristotle never dreamt that the nomenclature which
was in use in his time could ever become obscure;[142\16] hence he
has taken no precaution to enable his readers to recognize the
species of which he speaks; and in him and in other ancient authors,
it requires much labor and great felicity of divination to determine
what the names mean. The perception of this difficulty among modern
naturalists led to systems, and to nomenclature founded upon system;
but these did not come into {422} being immediately at the time of
which we speak; nor till the evil had grown to a more inconvenient
magnitude.
[Note 142\16: Cuvier, p. 17.]
_Period of Accumulation of Materials. Exotic Collections._--The
fishes of Europe were for some time the principal objects of study;
but those of distant regions soon came into notice.[143\16] In the
seventeenth century the Dutch conquered Brazil, and George Margrave,
employed by them, described the natural productions of the country,
and especially the fishes. Bontius, in like manner, described some
of those of Batavia. Thus these writers correspond to Romphius and
Rheede in the history of botany. Many others might be mentioned; but
we must hasten to the formation of systems, which is our main object
of attention.
[Note 143\16: Cuv. p. 43.]
_Epoch of the Fixation of Characters. Ray and Willoughby._--In
botany, as we have seen, though Ray was one of the first who
invented a connected system, he was preceded at a considerable
interval by Cæsalpinus, who had given a genuine solution of the same
problem. It is not difficult to assign reasons why a sound
classification should be discovered for plants at an earlier period
than for fishes. The vastly greater number of the known species, and
the facilities which belong to the study of vegetables, give the
botanist a great advantage; and there are numerical relations of a
most definite kind (for instance, the number of parts of the
seed-vessel employed by Cæsalpinus as one of the bases of his
system), which are tolerably obvious in plants, but which are not
easily discovered in animals. And thus we find that in ichthyology,
Ray, with his pupil and friend Willoughby, appears as the first
founder of a tenable system.[144\16]
[Note 144\16: Francisci Willoughbeii, Armigeri, _de Historia
Piscium_, libri iv. jussu et sumptibus Societatis Regiæ Londinensis
editi, &c. Totum opus recognovit, coaptavit, supplevit, librum etiam
primum et secundum adjecit Joh. Raius. Oxford, 1668.]
The first great division in this system is into _cartilaginous_ and
_bony_ fishes; a primary division, which had been recognized by
Aristotle, and is retained by Cuvier in his latest labors. The
subdivisions are determined by the general form of the fish (as long
or flat), by the teeth, the presence or absence of ventral fins, the
number of dorsal fins, and the nature of the spines of the fins, as
soft or prickly. Most of these characters have preserved their
importance in later systems; especially the last, which, under the
terms _malacopterygian_ and _acanthopterygian_, holds a place in the
best recent arrangements. {423}
That this system was a true first approximation to a solution of the
problem, appears to be allowed by naturalists. Although, says
Cuvier,[145\16] there are in it no genera well defined and well
limited, still in many places the species are brought together very
naturally, and in such a way that a few words of explanation would
suffice to form, from the groups thus presented to us, several of
the genera which have since been received. Even in botany, as we
have seen, genera were hardly maintained with any degree of
precision, till the binary nomenclature of Linnæus made this
division a matter of such immense convenience.
[Note 145\16: Cuvier, p. 57.]
The amount of this convenience, the value of a brief and sure
nomenclature, had not yet been duly estimated. The work of Willoughby
forms an epoch,[146\16] and a happy epoch, in the history of
ichthyology; for the science, once systematized, could distinguish the
new from the old, arrange methodically, describe clearly. Yet, because
Willoughby had no nomenclature of his own, and no fixed names for his
genera, his immediate influence was not great. I will not attempt to
trace this influence in succeeding authors, but proceed to the next
important step in the progress of system.
[Note 146\16: p. 58.]
_Improvement of the System. Artedi._--Peter Artedi was a countryman
and intimate friend of Linnæus; and rendered to ichthyology nearly
the same services which Linnæus rendered to botany. In his
_Philosophia Ichthyologica_, he analysed[147\16] all the interior
and exterior parts of animals; he created a precise terminology for
the different forms of which these parts are susceptible; he laid
down rules for the nomenclature of genera and species; besides his
improvements of the subdivisions of the class. It is impossible not
to be struck with the close resemblance between these steps, and
those which are due to the _Fundamenta Botanica_. The latter work
appeared in 1736, the former was published by Linnæus, after the
death of the author, in 1738; but Linnæus had already, as early as
1735, made use of Artedi's manuscripts in the ichthyological part of
his _Systema Naturæ_. We cannot doubt that the two young naturalists
(they were nearly of the same age), must have had a great influence
upon each other's views and labors; and it would be difficult now to
ascertain what portion of the peculiar merits of the Linnæan reform
was derived from Artedi. But we may remark that, in ichthyology at
least, Artedi appears to have been a naturalist of more original
views and profounder philosophy than his friend and editor, who
afterwards himself took up the subject. {424} The reforms of
Linnæus, in all parts of natural history, appear as if they were
mainly dictated by a love of elegance, symmetry, clearness, and
definiteness; but the improvement of the ichthyological system by
Artedi seems to have been a step in the progress to a natural
arrangement. His genera,[148\16] which are forty-five in number, are
so well constituted, that they have almost all been preserved; and
the subdivisions which the constantly-increasing number of species
has compelled his successors to introduce, have very rarely been
such that they have led to the transposition of his genera.
[Note 147\16: p. 20.]
[Note 148\16: Cuvier, p. 71.]
In its bases, however, Artedi's was an artificial system. His
characters were positive and decisive, founded in general upon the
number of rays of the membrane of the gills, of which he was the
first to mark the importance;--upon the relative position of the
fins, upon their number, upon the part of the mouth where the teeth
are found, upon the conformation of the scales. Yet, in some cases,
he has recourse to the interior anatomy.
Linnæus himself at first did not venture to deviate from the
footsteps of a friend, who, in this science, had been his master.
But in 1758, in the tenth edition of the _Systema Naturæ_, he chose
to depend upon himself and devised a new ichthyological method. He
divided some genera, united others, gave to the species trivial
names and characteristic phrases, and added many species to those of
Artedi. Yet his innovations are for the most part disapproved of by
Cuvier; as his transferring the _chondropterygian_ fishes of Artedi
to the class of reptiles, under the title of _Amphybia nantes_; and
his rejecting the distinction of acanthopterygian and
malacopterygian, which, as we have seen, had prevailed from the time
of Willoughby, and introducing in its stead a distribution founded
on the presence or absence of the ventral fins, and on their
situation with regard to the pectoral fins. "Nothing," says Cuvier,
"more breaks the true connexions of genera than these orders of
_apodes_, _jugulares_, _thoracici_, and _abdominales_."
Thus Linnæus, though acknowledging the value and importance of
natural orders, was not happy in his attempts to construct a system
which should lead to them. In his detection of good characters for
an artificial system he was more fortunate. He was always attentive
to number, as a character; and he had the very great merit[149\16]
of introducing into the classification the number of rays of the
fins of each species. This mark is one of great importance and use.
And this, as well as {425} other branches of natural history,
derived incalculable advantages from the more general merits of the
illustrious Swede;[150\16]--the precision of the characters, the
convenience of a well-settled terminology, the facility afforded by
the binary nomenclature. These recommendations gave him a
pre-eminence which was acknowledged by almost all the naturalists of
his time, and displayed by the almost universal adoption of his
nomenclature, in zoology, as well as in botany; and by the almost
exclusive employment of his distributions of classes, however
imperfect and artificial they might be.
[Note 149\16: p. 74.]
[Note 150\16: Cuvier, p. 85.]
And even[151\16] if Linnæus had had no other merit than the impulse
he gave to the pursuit of natural science, this alone would suffice
to immortalize his name. In rendering natural history easy, or at
least in making it appear so, he diffused a general taste for it.
The great took it up with interest; the young, full of ardor, rushed
forwards in all directions, with the sole intention of completing
his system. The civilized world was eager to build the edifice which
Linnæus had planned.
[Note 151\16: Ib. p. 88.]
This spirit, among other results, produced voyages of natural
historical research, sent forth by nations and sovereigns. George
the Third of England had the honor of setting the example in this
noble career, by sending out the expeditions of Byron, Wallis, and
Carteret, in 1765. These were followed by those of Bougainville,
Cook, Forster, and others. Russia also scattered several scientific
expeditions through her vast dominions; and pupils of Linnæus sought
the icy shores of Greenland and Iceland, in order to apply his
nomenclature to the productions of those climes. But we need not
attempt to convey any idea of the vast stores of natural historical
treasures which were thus collected from every part of the globe.
I shall not endeavor to follow Cuvier in giving an account of the
great works of natural history to which this accumulation of materials
gave rise; such as the magnificent work of Bloch on Fishes, which
appeared in 1782-1785; nor need I attempt, by his assistance, to
characterize or place in their due position the several systems of
classification proposed about this time. But in the course of these
various essays, the distinction of the artificial and natural methods
of classification came more clearly into view than before; and this is
a point so important to the philosophy of the subject, that we must
devote a few words to it. {426}
_Separation of the Artificial and Natural Methods in Ichthyology._--It
has already been said that all so-called _artificial methods_ of
classification must be natural, at least as to the narrowest members
of the system; thus the artificial Linnæan method is natural as to
species, and even as to genera. And on the other hand, all proposed
natural methods, so long as they remain unmodified, are artificial as
to their characteristic marks. Thus a Natural Method is an attempt to
provide positive and distinct _characters_ for the _wider_ as well as
for the narrower _natural groups_. These considerations are applicable
to zoology as well as to botany. But the question, how we know natural
groups before we find marks for them, was, in botany, as we have seen,
susceptible only of vague and obscure answers:--the mind forms them,
it was said, by taking the aggregate of all the characters; or by
establishing a subordination of characters. And each of these answers
had its difficulty, of which the solution appeared to be, that in
attempting to form natural orders we are really guided by a latent
undeveloped estimate of physiological relations. Now this principle,
which was so dimly seen in the study of vegetables, shines out with
much greater clearness when we come to the study of animals, in which
the physiological relations of the parts are so manifest that they
cannot be overlooked, and have so strong an attraction for our
curiosity that we cannot help having our judgments influenced by them.
Hence the superiority of natural systems in zoology would probably be
far more generally allowed than in botany; and no arrangement of
animals which, in a large number of instances, violated strong and
clear natural affinities, would be tolerated because it answered the
purpose of enabling us easily to find the name and place of the animal
in the artificial system. Every system of zoological arrangement may
be supposed to aspire to be a natural system. But according to the
various habits of the minds of systematizers, this object was pursued
more or less steadily and successfully; and these differences came
more and more into view with the increase of knowledge and the
multiplication of attempts.
Bloch, whose ichthyological labors have been mentioned, followed in
his great work the method of Linnæus. But towards the end of his
life he had prepared a general system, founded upon one single
numerical principle;--the number of fins; just as the sexual system
of Linnæus is founded upon the number of stamina; and he made his
subdivisions according to the position of the ventral and pectoral
fins; the same character which Linnæus had employed for his primary
{427} division. He could not have done better, says Cuvier,[152\16]
if his object had been to turn into ridicule all artificial methods,
and to show to what absurd combinations they may lead.
[Note 152\16: p. 108.]
Cuvier himself who always pursued natural systems with a singularly
wise and sagacious consistency, attempted to improve the
ichthyological arrangements which had been proposed before him. In
his _Règne Animal_, published in 1817, he attempts the problem of
arranging this class; and the views suggested to him, both by his
successes and his failures, are so instructive and philosophical,
that I cannot illustrate the subject better than by citing some of
them.
"The class of fishes," he says,[153\16] "is, of all, that which
offers the greatest difficulties, when we wish to subdivide it into
orders, according to fixed and obvious characters. After many
trials, I have determined on the following distribution, which in
some instances is wanting in precision, but which possesses the
advantage of keeping the natural families entire.
[Note 153\16: _Règne Animal_, vol. ii. p. 110.]
"Fish form two distinct series;--that of _chondropterygians_ or
_cartilaginous fish_, and that of _fish_ properly so called.
"The _first_ of these series has for its character, that the
palatine bones replace, in it, the bones of the upper jaw: moreover
the whole of its structure has evident analogies, which we shall
explain.
"It divides itself into three ORDERS:
"The CYCLOSTOMES, in which the jaws are soldered (_soudées_) into an
immovable ring, and the bronchiæ are open in numerous holes.
"The SELACIANS, which have the bronchiæ like the preceding, but not
the jaws.
"The STURONIANS, in which the bronchiæ are open as usual by a slit
furnished with an operculum.
"The second series, or that of _ordinary fishes_, offers me, in the
first place, a primary division, into those of which the maxillary
bone and the palatine arch are dovetailed (_engrenés_) to the skull.
Of these I make an order of PECTOGNATHS, divided into two families;
the _gymnodonts_ and the _scleroderms_.
"After these I have the fishes with complete jaws, but with bronchiæ
which, instead of having the form of combs, as in all the others,
have the form of a series of little tufts (_houppes_). Of these I
again form an order, which I call LOPHOBRANCHS, which only includes
one family. {428}
"There then remains an innumerable quantity of fishes, to which we
can no longer apply any characters except those of the exterior
organs of motion. After long examination, I have found that the
least bad of these characters is, after all, that employed by Ray
and Artedi, taken from the nature of the first rays of the dorsal
and of the anal fin. Thus ordinary fishes are divided into
MALACOPTERYGIANS, of which all the rays are soft, except sometimes
the first of the dorsal fin or the pectorals;--and
ACANTHOPTERYGIANS, which have always the first portion of the
dorsal, or of the first dorsal when there are two, supported by
spinous rays, and in which the anal has also some such rays, and the
ventrals, at least, each one.
"The former may be subdivided without inconvenience, according to
their ventral fins, which are sometimes situate behind the abdomen,
sometimes adherent to the apparatus of the shoulder, or, finally,
are sometimes wanting altogether.
"We thus arrive at the three orders of ABDOMINAL MALACOPTERYGIANS,
of SUBBRACHIANS, and of APODES; each of which includes some natural
families which we shall explain: the first, especially, is very
numerous.
"But this basis of division is absolutely impracticable with the
Acanthopterygians; and the problem of establishing among these any
other subdivision than that of the natural families has hitherto
remained for me insoluble. Fortunately several of these families
offer characters almost as precise as those which we could give to
true orders.
"In truth, we cannot assign to the families of fishes, ranks as
marked, as for example, to those of mammifers. Thus the
Chondropterygians on the one hand hold to reptiles by the organs of
the senses, and by those of generation in some; and they are related
to mollusks and worms by the imperfection of the skeleton in others.
"As to Ordinary Fishes, if any part of the organization is found
more developed in some than in others, there does not result from
this any pre-eminence sufficiently marked, or of sufficient
influence upon their whole system, to oblige us to consult it in the
methodical arrangement.
"We shall place them, therefore, nearly in the order in which we
have just explained their characters."
I have extracted the whole of this passage, because, though it is
too technical to be understood in detail by the general reader,
those who have followed with any interest the history of the
attempts at a natural classification in any department in nature,
will see here a fine example of the problems which such attempts
propose, of the {429} difficulties which it may present, and of the
reasonings, labors, cautions, and varied resources, by means of
which its solution is sought, when a great philosophical naturalist
girds himself to the task. We see here, most instructively, how
different the endeavor to frame such a natural system, is from the
procedure of an artificial system, which carries imperatively
through the whole of a class of organized beings, a system of marks
either arbitrary, or conformable to natural affinities in a partial
degree. And we have not often the advantage of having the reasons
for a systematic arrangement so clearly and fully indicated, as is
done here, and in the descriptions of the separate orders.
This arrangement Cuvier adhered to in all its main points, both in
the second edition of the _Règne Animal_, published in 1821, and in
his _Histoire Naturelle des Poissons_, of which the first volume was
published in 1828, but which unfortunately was not completed at the
time of his death. It may be supposed, therefore, to be in
accordance with those views of zoological philosophy, which it was
the business of his life to form and to apply; and in a work like
the present, where, upon so large a question of natural history, we
must be directed in a great measure by the analogy of the history of
science, and by the judgments which seem most to have the character
of wisdom, we appear to be justified in taking Cuvier's
ichthyological system as the nearest approach which has yet been
made to a natural method in that department.
The true natural method is only one: artificial methods, and even
good ones, there may be many, as we have seen in botany; and each of
these may have its advantages for some particular use. On some
methods of this kind, on which naturalists themselves have hardly
yet had time to form a stable and distinct opinion, it is not our
office to decide. But judging, as I have already said, from the
general analogy of the natural sciences, I find it difficult to
conceive that the ichthyological method of M. Agassiz, recently
propounded with an especial reference to fossil fishes, can be
otherwise than an artificial method. It is founded entirely on one
part of the animal, its scaly covering, and even on a single scale.
It does not conform to that which almost all systematic
ichthyologists hitherto have considered as a permanent natural
distinction of a high order; the distinction of bony and
cartilaginous fishes; for it is stated that each order contains
examples of both.[154\16] I do not know what general anatomical or
physiological {430} truths it brings into view; but they ought to be
very important and striking ones, to entitle them to supersede those
which led Cuvier to his system. To this I may add, that the new
ichthyological classification does not seem to form, as we should
expect that any great advance towards a natural system would form, a
connected sequel to the past history of ichthyology;--a step to
which anterior discoveries and improvements have led, and in which
they are retained.
[Note 154\16: Dr. Buckland's _Bridgewater Treatise_, p. 270.]
But notwithstanding these considerations, the method of M. Agassiz
has probably very great advantages for his purpose; for in the case
of fossil fish, the parts which are the basis of his system often
remain, when even the skeleton is gone. And we may here again refer
to a principle of the classificatory sciences which we cannot make
too prominent;--all arrangements and nomenclatures are good, which
enable us to assert general propositions. Tried by this test, we
cannot fail to set a high value on the arrangement of M. Agassiz;
for propositions of the most striking generality respecting fossil
remains of fish, of which geologists before had never dreamt, are
enunciated by means of his groups and names. Thus only the two first
orders, the _Placoïdians_ and _Ganoïdians_, existed before the
commencement of the cretaceous formation: the third and fourth
orders, the _Ctenoïdians_ and _Cycloïdians_, which contain
three-fourths of the eight thousand known species of living Fishes,
appear for the first time in the cretaceous formation: and other
geological relations of these orders, no less remarkable, have been
ascertained by M. Agassiz.
But we have now, I trust, pursued these sciences of classification
sufficiently far; and it is time for us to enter upon that higher
domain of Physiology to which, as we have said. Zoology so
irresistibly directs us.
[2nd Ed.] [I have retained the remarks which I ventured at first to
make on the System of M. Agassiz; but I believe the opinion of the
most philosophical ichthyologists to be that Cuvier's System was too
exclusively based on the internal skeleton, as Agassiz's was on the
external skeleton. In some degree both systems have been superseded,
while all that was true in each has been retained. Mr. Owen, in his
_Lectures on Vertebrata_ (1846), takes Cuvierian characters from the
endo-skeleton, Agassizian ones from the exo-skeleton, Linnæan ones
from the ventral fins, Müllerian ones from the air-bladder, and
combines them by the light of his own researches, with the view of
forming a system more truly natural than any preceding one.
As I have said above, naturalists, in their progress towards a
Natural {431} System, are guided by physiological relations,
latently in Botany, but conspicuously in Zoology. From the epoch of
Cuvier's _Règne Animal_, the progress of Systematic Zoology is
inseparably dependent on the progress of Comparative Anatomy. Hence
I have placed Cuvier's Classification of animal forms in the next
Book, which treats of Physiology.]
{{433}}
BOOK XVII.
_ORGANICAL SCIENCES._
HISTORY OF PHYSIOLOGY
AND
COMPARATIVE ANATOMY.
Fearful and wondrous is the skill which moulds
Our body's vital plan,
And from the first dim hidden germ unfolds
The perfect limbs of man.
Who, who can pierce the secret? tell us how
Something is drawn from naught,
Life from the inert mass? Who, Lord! but thou,
Whose hand the whole has wrought?
Of this corporeal substance, still to be,
Thine eye a survey took;
And all my members, yet unformed by thee,
Were written in thy book.
PSALM cxxxix. 13-16.
{{435}}
INTRODUCTION.
_Of the Organical Sciences_
THOUGH the general notion of _life_ is acknowledged by the most
profound philosophers to be dim and mysterious, even up to the
present time; and must, in the early stages of human speculation,
have been still more obscure and confused; it was sufficient, even
then, to give interest and connexion to men's observations upon
their own bodies and those of other animals. It was seen, that in
living things, certain peculiar processes were constantly repeated,
as those of breathing and of taking food, for example; and that a
certain conformation of the parts of the animal was subservient to
these processes; and thus were gradually formed the notions of
_Function_ and of _Organization_. And the sciences of which these
notions formed the basis are clearly distinguishable from all those
which we have hitherto considered. We conceive an _organized_ body
to be one in which the parts are there for the sake of the whole, in
a manner different from any mechanical or chemical connexion; we
conceive a _function_ to be not merely a process of change, but of
change connected with the general vital process. When mechanical or
chemical processes occur in the living body, they are instrumental
to, and directed by, the peculiar powers of life. The sciences which
thus consider organization and vital functions may be termed
_organical_ sciences.
When men began to speculate concerning such subjects, the general
mode of apprehending the process in the cases of some functions,
appeared to be almost obvious; thus it was conceived that the growth
of animals arose from their frame appropriating to itself a part of
the substance of the food through the various passages of the body.
Under the influence of such general conceptions, speculative men
were naturally led to endeavor to obtain more clear and definite
views of the course of each of such processes, and of the mode in
which the separate parts contributed to it. Along with the
observation of the living person, the more searching examination
which could be carried on in the dead body, and the comparison of
various kinds of animals, soon showed that this pursuit was rich in
knowledge and in interest. {436} Moreover, besides the interest
which the mere speculative faculty gave to this study, the Art of
Healing added to it a great practical value; and the effects of
diseases and of medicines supplied new materials and new motives for
the reasonings of the philosopher.
In this manner anatomy or physiology may be considered as a science
which began to be cultivated in the earliest periods of civilization.
Like most other ancient sciences, its career has been one of perpetual
though variable progress; and as in others, so in this, each step has
implied those which had been previously made, and cannot be understood
aright except we understand them. Moreover, the steps of this advance
have been very many and diverse; the cultivators of anatomy have in
all ages been numerous and laborious; the subject is one of vast
extent and complexity; almost every generation had added something to
the current knowledge of its details; and the general speculations of
physiologists have been subtle, bold, and learned. It must, therefore,
be difficult or impossible for a person who has not studied the
science with professional diligence and professional advantages, to
form just judgments of the value of the discoveries of various ages
and persons, and to arrange them in their due relation to each other.
To this we may add, that though all the discoveries which have been
made with respect to particular functions or organizations are
understood to be subordinate to one general science, the Philosophy of
Life, yet the principles and doctrines of this science nowhere exist
in a shape generally received and assented to among physiologists; and
thus we have not, in this science, the advantage which in some others
we have possessed;--of discerning the true direction of its first
movements, by knowing the point to which they ultimately tend;--of
running on beyond the earlier discoveries, and thus looking them in
the face, and reading their true features. With these disadvantages,
all that we can have to say respecting the history of Physiology must
need great indulgence on the part of the reader.
Yet here, as in other cases, we may, by guiding our views by those
of the greatest and most philosophical men who have made the subject
their study, hope to avoid material errors. Nor can we well evade
making the attempt. To obtain some simple and consistent view of the
progress of physiological science, is in the highest degree
important to the completion of our views of the progress of physical
science. For the physiological or organical sciences form a class to
which the classes already treated of, the mechanical, chemical, and
classificatory sciences, are subordinate and auxiliary. Again,
another {437} circumstance which makes physiology an important part
of our survey of human knowledge is, that we have here a science
which is concerned, indeed, about material combinations, but in
which we are led almost beyond the borders of the material world,
into the region of sensation and perception, thought and will. Such
a contemplation may offer some suggestions which may prepare us for
the transition from physical to metaphysical speculations.
In the survey which we must, for such purposes, take of the progress
of physiology, it is by no means necessary that we should exhaust
the subject, and attempt to give the history of every branch of the
knowledge of the phenomena and laws of living creatures. It will be
sufficient, if we follow a few of the lines of such researches,
which may be considered as examples of the whole. We see that life
is accompanied and sustained by many processes, which at first offer
themselves to our notice as separate functions, however they may
afterwards be found to be connected and identified; such are
feeling, digestion, respiration, the action of the heart and pulse,
generation, perception, voluntary motion. The analysis of any one of
these functions may be pursued separately. And since in this, as in
all genuine sciences, our knowledge becomes real and scientific,
only in so far as it is verified in particular facts, and thus
established in general propositions, such an original separation of
the subjects of research is requisite to a true representation of
the growth of real knowledge. The loose hypotheses and systems,
concerning the connexion of different vital faculties and the
general nature of living things, which have often been promulgated,
must be excluded from this part of our plan. We do not deny all
value and merit to such speculations; but they cannot be admitted in
the earlier stages of the history of physiology, treated of as an
inductive science. If the doctrine so propounded have a solid and
permanent truth, they will again come before us when we have
travelled through the range of more limited truths, and are prepared
to ascend with security and certainty into the higher region of
general physiological principles. If they cannot be arrived at by
such a road, they are then, however plausible and pleasing, no
portion of that real and progressive science with which alone our
history is concerned.
We proceed, therefore, to trace the establishment of some of the
more limited but certain doctrines of physiology. {438}
CHAPTER I.
DISCOVERY OF THE ORGANS OF VOLUNTARY MOTION.
_Sect._ 1.--_Knowledge of Galen and his Predecessors._
IN the earliest conceptions which men entertained of their power of
moving their own members, they probably had no thought of any
mechanism or organization by which this was effected. The foot and
the hand, no less than the head, were seen to be endowed with life;
and this pervading life seemed sufficiently to explain the power of
motion in each part of the frame, without its being held necessary
to seek out a special seat of the will, or instruments by which its
impulses were made effective. But the slightest inspection of
dissected animals showed that their limbs were formed of a curious
and complex collection of cordage, and communications of various
kinds, running along and connecting the bones of the skeleton. These
cords and communications we now distinguish as muscles, nerves,
veins, arteries, &c.; and among these, we assign to the muscles the
office of moving the parts to which they are attached, as cords move
the parts of a machine. Though this action of the muscles on the
bones may now appear very obvious, it was, probably, not at first
discerned. It is observed that Homer, who describes the wounds which
are inflicted in his battles with so much apparent anatomical
precision, nowhere employs the word _muscle_. And even Hippocrates
of Cos, the most celebrated physician of antiquity, is held to have
had no distinct conception of such an organ.[1\17] He always employs
the word _flesh_ when he means _muscle_, and the first explanation
of the latter word (μῦς) occurs in a spurious work ascribed to him.
For nerves, sinews, ligaments,[2\17] he used indiscriminately the
same terms; (τόνος or νεῦρον;) and of these nerves (νεῦρα) he
asserts that they contract the limbs. Nor do we find much more
distinctness on this subject even in Aristotle, a generation or two
later. "The origin of the νεῦρα," he says,[3\17] "is from the heart;
they connect {439} the bones, and surround the joints." It is clear
that he means here the muscles, and therefore it is with injustice
that he has been accused of the gross error of deriving the nerves
from the heart. And he is held to have really had the merit[4\17] of
discovering the nerves of sensation, which he calls the "canals of
the brain" (πόροι τοῦ ἐγκεφάλου); but the analysis of the mechanism
of motion is left by him almost untouched. Perhaps his want of sound
mechanical notions, and his constant straining after verbal
generalities, and systematic classifications of the widest kind,
supply the true account of his thus missing the solution of one of
the simplest problems of Anatomy.
[Note 1\17: Sprengel, _Geschichte der Arzneikunde_, i. 382.]
[Note 2\17: Sprengel, _Gesch. Arz._ i. 385.]
[Note 3\17: _Hist. Anim._ iii. 5.]
[Note 4\17: Ib. i. 456.]
In this, however, as in other subjects, his immediate predecessors
were far from remedying the deficiencies of his doctrines. Those who
professed to study physiology and medicine were, for the most part,
studious only to frame some general system of abstract principles,
which might give an appearance of connexion and profundity to their
tenets. In this manner the successors of Hippocrates became a
medical school, of great note in its day, designated as the
_Dogmatic_ school;[5\17] in opposition to which arose an _Empiric_
sect, who professed to deduce their modes of cure, not from
theoretical dogmas, but from experience. These rival parties
prevailed principally in Asia Minor and Egypt, during the time of
Alexander's successors,--a period rich in names, but poor in
discoveries; and we find no clear evidence of any decided advance in
anatomy, such as we are here attempting to trace.
[Note 5\17: Sprengel, _Gesch. Arz._ i. 583.]
The victories of Lucullus and Pompeius, in Greece and Asia, made the
Romans acquainted with the Greek philosophy; and the consequence
soon was, that shoals of philosophers, rhetoricians, poets, and
physicians[6\17] streamed from Greece, Asia Minor, and Egypt, to
Rome and Italy, to traffic their knowledge and their arts for Roman
wealth. Among these, was one person whose name makes a great figure
in the history of medicine, Asclepiades of Prusa in Bithynia. This
man appears to have been a quack, with the usual endowments of his
class;--boldness, singularity, a contemptuous rejection of all
previously esteemed opinions, a new classification of diseases, a
new list of medicines, and the assertion of some wonderful cures. He
would not, on such accounts, deserve a place in the history of
science, but that he became the founder of a new school, the
_Methodic_, which professed to hold itself separate both from the
Dogmatics and the Empirics. {440}
[Note 6\17: Sprengel, _Gesch. Arz._ ii. 5.]
I have noticed these schools of medicine, because, though I am not
able to state distinctly their respective merits in the cultivation
of anatomy, a great progress in that science was undoubtedly made
during their domination, of which the praise must, I conceive, be in
some way divided among them. The amount of this progress we are able
to estimate, when we come to the works of Galen, who flourished
under the Antonines, and died about A.D. 203. The following passage
from his works will show that this progress in knowledge was not
made without the usual condition of laborious and careful
experiment, while it implies the curious fact of such experiment
being conducted by means of family tradition and instruction, so as
to give rise to a _caste_ of dissectors. In the opening of his
Second Book _On Anatomical Manipulations_, he speaks thus of his
predecessors: "I do not blame the ancients, who did not write books
on anatomical manipulation; though I praise Marinus, who did. For it
was superfluous for them to compose such records for themselves or
others, while they were, from their childhood, exercised by their
parents in dissecting, just as familiarly as in writing and reading;
so that there was no more fear of their forgetting their anatomy,
than of forgetting their alphabet. But when grown men, as well as
children, were taught, this thorough discipline fell off; and, the
art being carried out of the family of the Asclepiads, and declining
by repeated transmission, books became necessary for the student."
That the general structure of the animal frame, as composed of bones
and muscles, was known with great accuracy before the time of Galen,
is manifest from the nature of the mistakes and deficiencies of his
predecessors which he finds it necessary to notice. Thus he
observes, that some anatomists have made one muscle into two, from
its having two heads;--that they have overlooked some of the muscles
in the face of an ape, in consequence of not skinning the animal
with their own hands;--and the like. Such remarks imply that the
current knowledge of this kind was tolerably complete. Galen's own
views of the general mechanical structure of an animal are very
clear and sound. The skeleton, he observes, discharges[7\17] the
office of the pole of a tent, or the walls of a house. With respect
to the action of the muscles, his views were anatomically and
mechanically correct; in some instances, he showed what this action
was, by severing the muscle.[8\17] He himself added considerably to
the existing knowledge of {441} this subject; and his discoveries
and descriptions, even of very minute parts of the muscular system,
are spoken of with praise by modern anatomists.[9\17]
[Note 7\17: _De Anatom. Administ._ i. 2.]
[Note 8\17: Sprengel, ii. 157.]
[Note 9\17: Sprengel, ii. 150.]
We may consider, therefore, that the doctrine of the muscular
system, as a collection of cords and sheets, by the contraction of
which the parts of the body are moved and supported, was firmly
established, and completely followed into detail, by Galen and his
predecessors. But there is another class of organs connected with
voluntary motion, the nerves, and we must for a moment trace the
opinions which prevailed respecting these. Aristotle, as we have
said, noticed some of the nerves of sensation. But Herophilus, who
lived in Egypt in the time of the first Ptolemy, distinguished
nerves as the organs of the will,[10\17] and Rufus, who lived in the
time of Trajan,[11\17] divides the nerves into sensitive and motive,
and derives them all from the brain. But this did not imply that men
had yet distinguished the nerves from the muscles. Even Galen
maintained that every muscle consists of a bundle of nerves and
sinews.[12\17] But the important points, the necessity of the nerve,
and the origination of all this apparatus of motion from the brain,
he insists upon with great clearness and force. Thus he proved the
necessity experimentally, by cutting through some of the bundles of
nerves,[13\17] and thus preventing the corresponding motions. And it
is, he says,[14\17] allowed by all, both physicians and
philosophers, that where the origin of the nerve is, there the seat
of the soul (ἡγημονικὸν τῆς ψυχῆς) must be: now this, he adds, is in
the brain, and not in the heart.
[Note 10\17: Ib. i. 534.]
[Note 11\17: Ib. ii. 67.]
[Note 12\17: Ibid. ii. 152. Galen, _De Motu Musc._, p. 553.]
[Note 13\17: Ib. 157.]
[Note 14\17: _De Hippocr. et Plat. Dog._ viii. 1.]
Thus the general construction and arrangement of the organization by
which voluntary motion is effected, was well made out at the time of
Galen, and is found distinctly delivered in his works. We cannot,
perhaps, justly ascribe any large portion of the general discovery
to him: indeed, the conception of the mechanism of the skeleton and
muscles was probably so gradually unfolded in the minds of
anatomical students, that it would be difficult, even if we knew the
labors of each person, to select one, as peculiarly the author of
the discovery. But it is clear that all those who did materially
contribute to the establishment of this doctrine, must have
possessed the qualifications which we find in Galen for such a task;
namely, clear mechanical views of what the {442} tensions of
collections of strings could do, and an exact practical acquaintance
with the muscular cordage which exists in the animal frame;--in
short, in this as in other instances of real advance in science,
there must have been clear ideas and real facts, unity of thought
and extent of observation, brought into contact.
_Sect._ 2.--_Recognition of Final Causes in Physiology. Galen._
THERE is one idea which the researches of the physiologist and the
anatomist so constantly force upon him, that he cannot help assuming
it as one of the guides of his speculations; I mean, the idea of a
_purpose_, or, as it is called in Aristotelian phrase, a _final
cause_, in the arrangements of the animal frame. It is impossible to
doubt that the motive nerves run along the limbs, _in order that_
they may convey to the muscles the impulses of the will; and that
the muscles are attached to the bones, _in order that_ they may move
and support them. This conviction prevails so steadily among
anatomists, that even when the use of any part is altogether
unknown, it is still taken for granted that it has some use. The
developement of this conviction,--of a purpose in the parts of
animals,--of a function to which each portion of the organization is
subservient,--contributed greatly to the progress of physiology; for
it constantly urged men forwards in their researches respecting each
organ, till some definite view of its purpose was obtained. The
assumption of hypothetical final causes in Physics may have been, as
Bacon asserts it to have been, prejudicial to science; but the
assumption of unknown final causes in Physiology, has given rise to
the science. The two branches of speculation, Physics and
Physiology, were equally led, by every new phenomenon, to ask their
question, "Why?" But, in the former case, "why" meant "through what
cause?" in the latter, "for what end?" And though it may be possible
to introduce into physiology the doctrine of efficient causes, such
a step can never obliterate the obligations which the science owes
to the pervading conception of a purpose contained in all
organization.
This conception makes its appearance very early. Indeed, without any
special study of our structure, the thought, that we are fearfully and
wonderfully made, forces itself upon men, with a mysterious
impressiveness, as a suggestion of our Maker. In this bearing, the
thought is developed to a considerable extent in the well-known
passage in Xenophon's _Conversations of Socrates_. Nor did it ever
lose its hold on sober-minded and instructed men. The Epicureans,
indeed, {443} held that the eye was not made for seeing, nor the ear
for hearing; and Asclepiades, whom we have already mentioned as an
impudent pretender, adopted this wild dogma.[15\17] Such assertions
required no labor. "It is easy," says Galen,[16\17] "for people like
Asclepiades, when they come to any difficulty, to say that Nature has
worked to no purpose." The great anatomist himself pursues his subject
in a very different temper. In a well-known passage, he breaks out
into an enthusiastic scorn of the folly of the atheistical
notions.[17\17] "Try," he says, "if you can imagine a shoe made with
half the skill which appears in the skin of the foot." Some one had
spoken of a structure of the human body which he would have preferred
to that which it now has. "See," Galen exclaims, after pointing out
the absurdity of the imaginary scheme, "see what brutishness there is
in this wish. But if I were to spend more words on such cattle,
reasonable men might blame me for desecrating my work, which I regard
as a religious hymn in honor of the Creator."
[Note 15\17: Sprengel, ii. 15.]
[Note 16\17: _De Usu Part._ v. 5, (on the kidneys.)]
[Note 17\17: _De Usu Part._ iii. 10.]
Galen was from the first highly esteemed as an anatomist. He was
originally of Pergamus; and after receiving the instructions of many
medical and philosophical professors, and especially of those of
Alexandria, which was then the metropolis of the learned and
scientific world, he came to Rome, where his reputation was soon so
great as to excite the envy and hatred of the Roman physicians. The
emperors Marcus Aurelius and Lucius Verus would have retained him
near them; but he preferred pursuing his travels, directed
principally by curiosity. When he died, he left behind him numerous
works, all of them of great value for the light they throw on the
history of anatomy and medicine; and these were for a long period
the storehouse of all the most important anatomical knowledge which
the world possessed. In the time of intellectual barrenness and
servility, among the Arabians and the Europeans of the dark ages,
the writings of Galen had almost unquestioned authority;[18\17] and
it was only by an uncommon effort of independent thinking that
Abdollatif ventured to assert, that even Galen's assertions must
give way to the evidence of the senses. In more modern times, when
Vesalius, in the sixteenth century, accused Galen of mistakes, he
drew upon himself the hostility of the whole body of physicians. Yet
the mistakes were such as might have {444} been pointed out and
confessed[19\17] without acrimony, if, in times of revolution,
mildness and moderation were possible; but an impatience of the
superstition of tradition on the part of the innovators, and an
alarm of the subversion of all recognized truths on the part of the
established teachers, inflame and pervert all such discussions.
Vesalius's main charge against Galen is, that his dissections were
performed upon animals, and not upon the human body. Galen himself
speaks of the dissection of apes as a very familiar employment, and
states that he killed them by drowning. The natural difficulties
which, in various ages, have prevented the unlimited prosecution of
human dissection, operated strongly among the ancients, and it would
have been difficult, under such circumstances, to proceed more
judiciously than Galen did.
[Note 18\17: Sprengel, ii. 359.]
[Note 19\17: Cuv. _Leçons sur l'Hist. des Sc. Nat._ p. 25.]
I shall now proceed to the history of the discovery of another and
less obvious function, the circulation of the blood, which belongs
to modern times.
CHAPTER II.
DISCOVERY OF THE CIRCULATION OF THE BLOOD.
_Sect._ 1.--_Prelude to the Discovery._
THE blood-vessels, the veins and arteries, are as evident and
peculiar in their appearance as the muscles; but their function is
by no means so obvious. Hippocrates[20\17] did not discriminate
Veins and Arteries; both are called by the same name (φλέβες) and
the word from which artery comes (ἀρτηρίη) means, in his works, the
windpipe. Aristotle, scanty as was his knowledge of the vessels of
the body, has yet the merit of having traced the origin of all the
veins to the heart. He expressly contradicts those of his
predecessors who had derived the veins from the head;[21\17] and
refers to dissection for the proof. If the book _On the Breath_ be
genuine (which is doubted), Aristotle was aware of the distinction
between veins and arteries. "Every artery," {445} it is there
asserted, "is accompanied by a vein; the former are filled only with
breath or air."[22\17] But whether or no this passage be
Aristotle's, he held opinions equally erroneous; as, that the
windpipe conveys air into the heart.[23\17] Galen[24\17] was far
from having views respecting the blood-vessels, as sound as those
which he entertained concerning the muscles. He held the liver to be
the origin of the veins, and the heart of the arteries. He was,
however, acquainted with their junctions, or _anastomoses_. But we
find no material advance in the knowledge of this subject, till we
overleap the blank of the middle ages, and reach the dawn of modern
science.
[Note 20\17: Sprengel, i. 383.]
[Note 21\17: _Hist. Animal._ iii. 3.]
[Note 22\17: _De Spiritu_, v. 1078.]
[Note 23\17: Spr. i. 501.]
[Note 24\17: Ib. ii. 152.]
The father of modern anatomy is held to be Mondino,[25\17] who
dissected and taught at Bologna in 1315. Some writers have traced in
him the rudiments of the doctrine of the circulation of the blood;
for he says that the heart transmits blood to the lungs. But it is
allowed, that he afterwards destroys the merit of his remark, by
repeating the old assertion that the left ventricle ought to contain
spirit or air, which it generates from the blood.
[Note 25\17: _Encyc. Brit._ 692. Anatomy.]
Anatomy was cultivated with great diligence and talent in Italy by
Achillini, Carpa, and Messa, and in France by Sylvius and Stephanus
(Dubois and Etienne). Yet still these empty assumptions respecting
the heart and blood-vessels kept their ground. Vesalius, a native of
Brussels, has been termed the founder of human anatomy, and his
great work _De Humani Corporis Fabricâ_ is, even yet, a splendid
monument of art, as well as science. It is said that his figures
were designed by Titian; and if this be not exactly true, says
Cuvier,[26\17] they must, at least, be from the pencil of one of the
most distinguished pupils of the great painter; for to this day,
though we have more finished drawings, we have no designs that are
more artist-like. Fallopius, who succeeded Vesalius at Padua, made
some additions to the researches of his predecessor; but in his
treatise _De Principio Venarum_, it is clearly seen[27\17] that the
circulation of the blood was unknown to him. Eustachius also, whom
Cuvier groups with Vesalius and Fallopius, as the three great
founders of modern anatomy, wrote a treatise on the vein
_azygos_[28\17] which is a little treatise on comparative anatomy;
but the discovery of the functions of the veins came from a
different quarter. {446}
[Note 26\17: _Leçons sur l'Hist. des Sc. Nat._ p. 21.]
[Note 27\17: Cuv. _Sc. Nat._ p. 32.]
[Note 28\17: Ib. p. 34.]
The unfortunate Servetus, who was burnt at Geneva as a heretic in
1553, is the first person who speaks distinctly of the small
circulation, or that which carries the blood from the heart to the
lungs, and back again to the heart. His work entitled _Christianismi
Restitutio_ was also burnt; and only two copies are known to have
escaped the flames. It is in this work that he asserts the doctrine
in question, as a collateral argument or illustration of his
subject. "The communication between the right and left ventricle of
the heart, is made," he says, "not as is commonly believed, through
the partition of the heart, but by a remarkable artifice (_magno
artificio_) the blood is carried from the right ventricle by a long
circuit through the lungs; is elaborated by the lungs, made yellow,
and transfused from the _vena arteriosa_ into the _arteria venosa_."
This truth is, however, mixed with various of the traditional
fancies concerning the "_vital spirit_, which has its origin in the
left ventricle." It may be doubted, also, how far Servetus formed
his opinion upon conjecture, and on a hypothetical view of the
formation of this vital spirit. And we may, perhaps, more justly
ascribe the real establishment of the pulmonary circulation as an
inductive truth, to Realdus Columbus, a pupil and successor of
Vesalius at Padua, who published a work _De Re Anatomicâ_ in 1559,
in which he claims this discovery as his own.[29\17]
[Note 29\17: _Encyc. Brit._]
Andrew Cæsalpinus, who has already come under our notice as one of
the fathers of modern inductive science, both by his metaphysical
and his physical speculations, described the pulmonary circulation
still more completely in his _Quæstiones Peripateticæ_, and even
seemed to be on the eve of discovering the great circulation; for he
remarked the swelling of veins below ligatures, and inferred from it
a refluent motion of blood in these vessels.[30\17] But another
discovery of structure was needed, to prepare the way for this
discovery of function; and this was made by Fabricius of
Acquapendente, who succeeded in the grand list of great professors
at Padua, and taught there for fifty years.[31\17] Sylvius had
discovered the existence of the valves of the veins; but Fabricius
remarked that they are all turned towards the heart. Combining this
disposition with that of the valves of the heart, and with the
absence of valves in the arteries, he might have come to the
conclusion[32\17] that the blood moves in a different direction in
the arteries and in the veins, and might thus have discovered the
circulation: but this glory was reserved for William Harvey: so true
{447} is it, observes Cuvier, that we are often on the brink of a
discovery without suspecting that we are so;--so true is it, we may
add, that a certain succession of time and of persons is generally
necessary to familiarize men with one thought, before they can
advance to that which is the next in order.
[Note 30\17: Ib.]
[Note 31\17: Cuv. p. 44.]
[Note 32\17: p. 45.]
_Sect._ 2.--_The Discovery of the Circulation made by Harvey._
WILLIAM HARVEY was born in 1578, at Folkestone in Kent.[33\17] He
first studied at Cambridge: he afterwards went to Padua, where the
celebrity of Fabricius of Acquapendente attracted from all parts
those who wished to be instructed in anatomy and physiology. In this
city, excited by the discovery of the valves of the veins, which his
master had recently made, and reflecting on the direction of the
valves which are at the entrance of the veins into the heart, and at
the exit of the arteries from it, he conceived the idea of making
experiments, in order to determine what is the course of the blood
in its vessels. He found that when he tied up veins in various
animals, they swelled below the ligature, or in the part furthest
from the heart; while arteries, with a like ligature, swelled on the
side next the heart. Combining these facts with the direction of the
valves, he came to the conclusion that the blood is impelled, by the
left side of the heart, in the arteries to the extremities, and
thence returns by the veins into the right side of the heart. He
showed, too, how this was confirmed by the phenomena of the pulse,
and by the results of opening the vessels. He proved, also, that the
circulation of the lungs is a continuation of the larger
circulation; and thus the whole doctrine of the double circulation
was established.
[Note 33\17: Cuv. p. 51.]
Harvey's experiments had been made in 1616 and 1618; it is commonly
said that he first promulgated his opinion in 1619; but the
manuscript of the lectures, delivered by him as lecturer to the
College of Physicians, is extant in the British Museum, and,
containing the propositions on which the doctrine is founded, refers
them to April, 1616. It was not till 1628 that he published, at
Frankfort, his _Exercitatio Anatomica de Motu Cordis et Sanguinis_;
but he there observes that he had for above nine years confirmed and
illustrated his opinion in his lectures, by arguments grounded upon
ocular demonstrations. {448}
_Sect._ 3.--_Reception of the Discovery._
WITHOUT dwelling long upon the circumstances of the general reception
of this doctrine, we may observe that it was, for the most part,
readily accepted by his countrymen, but that abroad it had to
encounter considerable opposition. Although, as we have seen, his
predecessors had approached so near to the discovery, men's minds were
by no means as yet prepared to receive it. Several physicians denied
the truth of the opinion, among whom the most eminent was Riolan,
professor at the Collège de France. Other writers, as usually happens
in the case of great discoveries, asserted that the doctrine was
ancient, and even that it was known to Hippocrates. Harvey defended
his opinion with spirit and temper; yet he appears to have retained a
lively recollection of the disagreeable nature of the struggles in
which he was thus involved. At a later period of his life, Ent,[34\17]
one of his admirers, who visited him, and urged him to publish the
researches on generation, on which he had long been engaged, gives
this account of the manner in which he received the proposal: "And
would you then advise me, (smilingly replies the doctor,) to quit the
tranquillity of this haven, wherein I now calmly spend my days, and
again commit myself to the unfaithful ocean? You are not ignorant how
great troubles my lucubrations, formerly published, have raised.
Better it is, certainly, at some time, to endeavor to grow wise at
home in private, than by the hasty divulgation of such things to the
knowledge whereof you have attained with vast labor, to stir up
tempests that may deprive you of your leisure and quiet for the
future."
[Note 34\17: Epist. Dedic. to _Anatom. Exercit._]
His merits were, however, soon generally recognized. He was[35\17]
made physician to James the First, and afterwards to Charles the
First, and attended that unfortunate monarch in the civil war. He
had the permission of the parliament to accompany the king on his
leaving London; but this did not protect him from having his house
plundered in his absence, not only of its furniture, but, which he
felt more, of the records of his experiments. In 1652, his brethren
of the College of Physicians placed a marble bust of him in their
hall, with an inscription recording his discoveries; and two years
later, he was nominated to the office of President of the College,
which however he {449} declined in consequence of his age and
infirmities. His doctrine soon acquired popular currency; it was,
for instance, taken by Descartes[36\17] as the basis of his
physiology in his work _On Man_; and Harvey had the pleasure, which
is often denied to discoverers, of seeing his discovery generally
adopted during his lifetime.
[Note 35\17: _Biog. Brit._]
[Note 36\17: Cuv. 53.]
_Sect._ 4.--_Bearing of the Discovery on the Progress of Physiology._
IN considering the intellectual processes by which Harvey's
discoveries were made, it is impossible not to notice, that the
recognition of a creative purpose, which, as we have said, appears
in all sound physiological reasonings, prevails eminently here. "I
remember," says Boyle, "that when I asked our famous Harvey what
were the things that induced him to think of a circulation of the
blood, he answered me, that when he took notice that the valves in
the veins of so many parts of the body were so placed, that they
gave a free passage to the blood towards the heart, but opposed the
passage of the venal blood the contrary way; he was incited to
imagine that so provident a cause as Nature had not placed so many
valves without design; and no design seemed more probable than that
the blood should be sent through the arteries, and return through
the veins, whose valves did not oppose its course that way."
We may notice further, that this discovery implied the usual
conditions, distinct general notions, careful observation of many
facts, and the mental act of bringing together these elements of
truth. Harvey must have possessed clear views of the motions and
pressures of a fluid circulating in ramifying tubes, to enable him
to see how the position of valves, the pulsation of the heart, the
effects of ligatures, of bleeding, and of other circumstances, ought
to manifest themselves in order to confirm his view. That he
referred to a multiplied and varied experience for the evidence that
it was so confirmed, we have already said. Like all the best
philosophers of his time, he insists rigidly upon the necessity of
such experience. "In every science," he says,[37\17] "be it what it
will, a diligent observation is requisite, and sense itself must be
frequently consulted. We must not rely upon other men's experience,
but our own, without which no man is a proper disciple of any part
of natural knowledge." And by publishing his experiments, he trusts,
he adds, that he has enabled his reader "to be an equitable {450}
umpire between Aristotle and Galen;" or rather, he might have said,
to see how, in the promotion of science, sense and reason,
observation and invention, have a mutual need of each other.
[Note 37\17: _Generation of Animals_, Pref.]
We may observe further, that though Harvey's glory, in the case now
before us, rested upon his having proved the reality of certain
mechanical movements and actions in the blood, this discovery, and
all other physiological truths, necessarily involved the assumption
of some peculiar agency belonging to living things, different both
from mechanical agency, and from chemical; and in short, something
_vital_, and not physical merely. For when it was seen that the
pulsation of the heart, its _systole_ and _diastole_, caused the
circulation of the blood, it might still be asked, what force caused
this constantly-recurring contraction and expansion. And again,
circulation is closely connected with respiration; the blood is, by
the circulation, carried to the lungs, and is there, according to
the expression of Columbus and Harvey, mixed with air. But by what
mechanism does this _mixture_ take place, and what is the real
nature of it? And when succeeding researches had enabled
physiologists to give an answer to this question, as far as chemical
relations go, and to say, that the change consists in the
abstraction of the carbon from the blood by means of the oxygen of
the atmosphere; they were still only led to ask further, how this
chemical change was effected, and how such a change of the blood
fitted it for its uses. Every function of which we explain the
course, the mechanism, or the chemistry, is connected with other
functions,--is subservient to them, and they to it; and all together
are parts of the general vital system of the animal, ministering to
its life, but deriving their activity from the life. Life is not a
collection of forces, or polarities, or affinities, such as any of
the physical or chemical sciences contemplate; it has powers of its
own, which often supersede those subordinate relations; and in the
cases where men have traced such agents in the animal frame, they
have always seen, and usually acknowledged, that these agents were
ministerial to some higher agency, more difficult to trace than
these, but more truly the cause of the phenomena.
The discovery of the mechanical and chemical conditions of the vital
functions, as a step in physiology, may be compared to the discovery
of the laws of phenomena in the heavens by Kepler and his
predecessors, while the discovery of the force by which they were
produced was still reserved in mystery for Newton to bring to light.
The subordinate relation of the facts, their **dependence on space
and time, their reduction to order and cycle, had been fully
performed; but the {451} reference of them to distinct ideas of
causation, their interpretation as the results of mechanical force,
was omitted or attempted in vain. The very notion of such Force, and
of the manner in which motions were determined by it, was in the
highest degree vague and vacillating; and a century was requisite,
as we have seen, to give to the notion that clearness and fixity
which made the Mechanics of the Heavens a possible science. In like
manner, the notion of Life, and of Vital Forces, is still too
obscure to be steadily held. We cannot connect it distinctly with
severe inductions from facts. We can trace the motions of the animal
fluids as Kepler traced the motions of the planets; but when we seek
to render a reason for these motions, like him, we recur to terms of
a wide and profound, but mysterious import; to Virtues, Influences,
undefined Powers. Yet we are not on this account to despair. The
very instance to which I am referring shows us how rich is the
promise of the future. Why, says Cuvier,[38\17] may not Natural
History one day have its Newton? The idea of the vital forces may
gradually become so clear and definite as to be available in
science; and future generations may include, in their physiology,
propositions elevated as far above the circulation of the blood, as
the doctrine of universal gravitation goes beyond the explanation of
the heavenly motions by epicycles.
[Note 38\17: _Ossem. Foss._ Introd.]
If, by what has been said, I have exemplified sufficiently the
nature of those steps in physiology, which, like the discovery of
the Circulation, give an explanation of the process of some of the
animal functions, it is not necessary for me to dwell longer on the
subject; for to write a history, or even a sketch of the history of
Physiology, would suit neither my powers nor my purpose. Some
further analysis of the general views which have been promulgated by
the most eminent physiologists, may perhaps be attempted in treating
of the Philosophy of Inductive Science; but the estimation of the
value of recent speculations and investigations must be left to
those who have made this vast subject the study of their lives. A
few brief notices may, however, be here introduced. {452}
CHAPTER III.
DISCOVERY OF THE MOTION OF THE CHYLE, AND CONSEQUENT SPECULATIONS.
_Sect._ 1.--_The Discovery of the Motion of the Chyle._
IT may have been observed in the previous course of this History of
the Sciences, that the discoveries in each science have a peculiar
physiognomy: something of a common type may be traced in the
progress of each of the theories belonging to the same department of
knowledge. We may notice something of this common form in the
various branches of physiological speculation. In most, or all of
them, we have, as we have noticed the case to be with respect to the
circulation of the blood, clear and certain discoveries of
mechanical and chemical processes, succeeded by speculations far
more obscure, doubtful, and vague, respecting the relation of these
changes to the laws of life. This feature in the history of
physiology may be further instanced, (it shall be done very
briefly), in one or two other cases. And we may observe, that the
lesson which we are to collect from this narrative, is by no means
that we are to confine ourselves to the positive discovery, and
reject all the less clear and certain speculations. To do this,
would be to lose most of the chances of ulterior progress; for
though it may be, that our conceptions of the nature of organic life
are not yet sufficiently precise and steady to become the guides to
positive inductive truths, still the only way in which these
peculiar physiological ideas can be made more distinct and precise,
and thus brought more nearly into a scientific form, is by this
struggle with our ignorance or imperfect knowledge. This is the
lesson we have learnt from the history of physical astronomy and
other sciences. We must strive to refer facts which are known and
understood, to higher principles, of which we cannot doubt the
existence, and of which, in some degree, we can see the place;
however dim and shadowy may be the glimpses we have hitherto been
able to obtain of their forms. We may often fail in such attempts,
but without the attempt we can never succeed. {453}
That the food is received into the stomach, there undergoes a change
of its consistence, and is then propelled along the intestines, are
obvious facts in the animal economy. But a discovery made in the
course of the seventeenth century brought into clearer light the
sequel of this series of processes, and its connexion with other
functions. In the year 1622, Asellius or Aselli[39\17] discovered
certain minute vessels, termed _lacteals_, which absorb a white
liquid (the _chyle_) from the bowels, and pour it into the blood.
These vessels had, in fact, been discovered by Eristratus, in the
ancient world,[40\17] in the time of Ptolemy; but Aselli was the
first modern who attended to them. He described them in a treatise
entitled _De Venis Lacteis, cum figuris elegantissimis_, printed at
Milan in 1627, the year after the death of the author. The work is
remarkable as the first which exhibits _colored_ anatomical figures;
the arteries and veins are represented in red, the lacteals in black.
[Note 39\17: Mayo, _Physiology_, p. 156.]
[Note 40\17: Cuv. _Hist. Sc._ p. 50.]
Eustachius,[41\17] at an earlier period, had described (in the
horse) the thoracic duct by which the chyle is poured into the
subclavian vein, on the right side of the neck. But this description
did not excite so much notice as to prevent its being forgotten, and
rediscovered in 1550, after the knowledge of the circulation of the
blood had given more importance to such a discovery. Up to this
time,[42\17] it had been supposed that the lacteals carried the
chyle to the liver, and that the blood was manufactured there. This
opinion had prevailed in all the works of the ancients and moderns;
its falsity was discovered by Pecquet, a French physician, and
published in 1651, in his _New Anatomical Experiments_; in which are
discovered a receptacle of the chyle, unknown till then, and the
vessel which conveys it to the subclavian vein. Pecquet himself and
other anatomists, soon connected this discovery with the doctrine,
then recently promulgated, of the circulation of the blood. In 1665,
these vessels, and the _lymphatics_ which are connected with them,
were further illustrated by Ruysch in his exhibition of their
valves. (_Dilucidatio valvularum in vasis lymphaticis et lacteis_.)
[Note 41\17: Cuv. _Hist._ p. 34.]
[Note 42\17: Ib. p. 365.]
_Sect._ 2.--_The Consequent Speculations. Hypotheses of Digestion._
THUS it was shown that aliments taken into the stomach are, by its
action, made to produce _chyme_; from the chyme, gradually changed
{454} in its progress through the intestines, _chyle_ is absorbed by
the lacteals; and this, poured into the blood by the thoracic duct,
repairs the waste and nourishes the growth of the animal. But by
what powers is the food made to undergo these transformations? Can
we explain them on mechanical or on chemical principles? Here we
come to a part of physiology less certain than the discovery of
vessels, or of the motion of fluids. We have a number of opinions on
this subject, but no universally acknowledged truth. We have a
collection of _Hypotheses of Digestion_ and _Nutrition_.
I shall confine myself to the former class; and without dwelling
long upon these, I shall mention some of them. The philosophers of
the Academy _del Cimento_, and several others, having experimented
on the stomach of gallinaceous birds, and observed the astonishing
force with which it breaks and grinds substances, were led to
consider the digestion which takes place in the stomach as a kind of
_trituration_.[43\17] Other writers thought it was more properly
described as _fermentation_; others again spoke of it as a
_putrefaction_. Varignon gave a merely physical account of the first
part of the process, maintaining that the division of the aliments
was the effect of the disengagement of the air introduced into the
stomach, and dilated by the heat of the body. The opinion that
digestion is a _solution_ of the food by the gastric juice has been
more extensively entertained.
[Note 43\17: Bourdon, _Physiol. Comp._ p. 514.]
Spallanzani and others made many experiments on this subject. Yet it
is denied by the best physiologists, that the changes of digestion
can be adequately represented as chemical changes only. The nerves
of the stomach (the _pneumo-gastric_) are said to be essential to
digestion. Dr. Wilson Philip has asserted that the influence of
these nerves, when they are destroyed, may be replaced by a galvanic
current.[44\17] This might give rise to a supposition that digestion
depends on galvanism. Yet we cannot doubt that all these
hypotheses,--mechanical, physical, chemical, galvanic--are
altogether insufficient. "The stomach must have," as Dr. Prout
says,[45\17] "the power of {455} organizing and vitalizing the
different elementary substances. It is impossible to imagine that
this organizing agency of the stomach can be chemical. This agency
is _vital_, and its nature completely unknown."
[Note 44\17: Müller (_Manual of Physiology_, B. iii. Sect. 1, Chap.
iii.) speaks of Dr. Wilson Philip's assertion that the nerves of the
stomach being cut, and a galvanic current kept up in them, digestion
is still accomplished. He states that he and other physiologists
have repeated such experiments on an extensive scale, and have found
no effect of this kind.]
[Note 45\17: _Bridgewater Tr._ p. 493.]
CHAPTER IV.
EXAMINATION OF THE PROCESS OF REPRODUCTION IN ANIMALS AND PLANTS,
AND CONSEQUENT SPECULATIONS.
_Sect._ 1.--_The Examination of the Process of Reproduction in
Animals._
IT would not, perhaps, be necessary to give any more examples of
what has hitherto been the general process of investigations on each
branch of physiology; or to illustrate further the combination which
such researches present, of certain with uncertain knowledge;--of
solid discoveries of organs and processes, succeeded by indefinite
and doubtful speculation concerning vital forces. But the
reproduction of organized beings is not only a subject of so much
interest as to require some notice, but also offers to us laws and
principles which include both the vegetable and the animal kingdom;
and which, therefore, are requisite to render intelligible the most
general views to which we can attain, respecting the world of
organization.
The facts and laws of reproduction were first studied in detail in
animals. The subject appears to have attracted the attention of some
of the philosophers of antiquity in an extraordinary degree: and
indeed we may easily imagine that they hoped, by following this
path, if any, to solve the mystery of creation. Aristotle appears to
have pursued it with peculiar complacency; and his great work _On
animals_ contains[46\17] an extraordinary collection of curious
observations relative to this subject. He had learnt the modes of
reproduction of most of the animals with which he was acquainted;
and his work is still, as a writer of our own times has said,[47\17]
"original after so many copies, and young after two thousand years."
His observations referred principally to the external circumstances
of generation: the anatomical examination was {456} left to his
successors. Without dwelling on the intermediate labors, we come to
modern times, and find that this examination owes its greatest
advance to those who had the greatest share in the discovery of the
circulation of the blood;--Fabricius of Acquapendente, and Harvey.
The former[48\17] published a valuable work on the Egg and the
Chick. In this are given, for the first time, figures representing
the developement of the chick, from its almost imperceptible
beginning, to the moment when it breaks the shell. Harvey pursued
the researches of his teacher. Charles[49\17] the First had supplied
him with the means of making the experiments which his purpose
required, by sacrificing a great number of the deer in Windsor Park
in the state of gestation: but his principal researches were those
respecting the egg, in which he followed out the views of Fabricius.
In the troubles which succeeded the death of the unfortunate Charles
the house of Harvey was pillaged; and he lost the whole of the
labors he had bestowed on the generation of insects. His work,
_Exercitationes de Generatione Animalium_, was published at London
in 1651; it is more detailed and perfect than that of Fabricius; but
the author was prevented by the unsettled condition of the country
from getting figures engraved to accompany his descriptions.
[Note 46\17: Bourdon, p. 161.]
[Note 47\17: Ib. p. 101.]
[Note 48\17: Cuv. _Hist. Sc. Nat._ p. 46.]
[Note 49\17: Ib. p. 53.]
Many succeeding anatomists pursued the examination of the series of
changes in generation, and of the organs which are concerned in
them, especially Malpighi, who employed the microscope in this
investigation, and whose work on the Chick was published in 1673. It
is impossible to give here any general view of the result of these
laborious series of researches: but we may observe, that they led to
an extremely minute and exact survey of all the parts of the fœtus,
its envelopes and appendages, and, of course, to a designation of
these by appropriate names. These names afterwards served to mark
the attempts which were made to carry the analogy of animal
generation into the vegetable kingdom.
There is one generalization of Harvey which deserves notice.[50\17]
He was led by his researches to the conclusion, that all living
things may be properly said to come from eggs: "Omne vivum ex ovo."
Thus not only do oviparous animals produce by means of eggs, but in
those which are viviparous, the process of generation begins with
the developement of a small vesicle, which comes from the ovary, and
which exists before the embryo: and thus viviparous or
suckling-beasts, {457} notwithstanding their name, are born from
eggs, as well as birds, fishes, and reptiles.[51\17] This principle
also excludes that supposed production of organized beings without
parents (of worms in corrupted matter, for instance,) which was
formerly called _spontaneous generation_; and the best physiologists
of modern times agree in denying the reality of such a mode of
generation.[52\17]
[Note 50\17: Exerc. lxiii.]
[Note 51\17: Bourdon, p. 221.]
[Note 52\17: Ib. p. 49.]
_Sect._ 2.--_The Examination of the Process of Reproduction in
Vegetables._
THE extension of the analogies of animal generation to the vegetable
world was far from obvious. This extension was however made;--with
reference to the embryo plant, principally by the microscopic
observers, Nehemiah Grew, Marcello Malpighi, and Antony
Leeuwenhoek;--with respect to the existence of the sexes, by Linnæus
and his predecessors.
The microscopic labors of Grew and Malpighi were patronized by the
Royal Society of London in its earliest youth. Grew's book, _The
Anatomy of Plants_, was ordered to be printed in 1670. It contains
plates representing extremely well the process of germination in
various seeds, and the author's observations exhibit a very clear
conception of the relation and analogies of different portions of
the seed. On the day on which the copy of this work was laid before
the Society, a communication from Malpighi of Bologna, _Anatomes
Plantarum Idea_, stated his researches, and promised figures which
should illustrate them. Both authors afterwards went on with a long
train of valuable observations, which they published at various
times, and which contain much that has since become a permanent
portion of the science.
Both Grew and Malpighi were, as we have remarked, led to apply to
vegetable generation many terms which imply an analogy with the
generation of animals. Thus, Grew terms the innermost coat of the
seed, the _secundine_; speaks of the _navel-fibres_, &c. Many more
such terms have been added by other writers. And, as has been
observed by a modern physiologist,[53\17] the resemblance is
striking. Both in the vegetable seed and in the fertilized animal
egg, we have an _embryo_, _chalazæ_, a _placenta_, an _umbilical
cord_, a _cicatricula_, an _amnios_, _membranes_, _nourishing
vessels_. The _cotyledons_ of the seed are the equivalent of the
_vitellus_ of birds, or of the _umbilical vesicle_ of
**suckling-beasts: {458} the _albumen_ or _perisperm_ of the grain is
analogous to the _white of the egg_ of birds, or the _allantoid_ of
viviparous animals.
[Note 53\17: Ib. p. 384.]