of which is occupied by a large oval mass called the “nucleus;” while,
at its hinder end, is a “contractile vacuole,” conspicuous by its
regular rhythmic appearances and disappearances. Obviously, although
the _Colpoda_ is not a monad, it differs from one only in subordinate
details. Moreover, under certain conditions, it becomes quiescent,
incloses itself in a delicate case or _cyst_, and then divides into
two, four, or more portions, which are eventually set free and swim
about as active _Colpodæ_.
But this creature is an unmistakable animal, and full-sized _Colpodæ_
may be fed as easily as one feeds chickens. It is only needful to
diffuse very finely ground carmine through the water in which they
live, and, in a very short time, the bodies of the _Colpodæ_ are
stuffed with the deeply-coloured granules of the pigment.
And if this were not sufficient evidence of the animality of _Colpoda_,
there comes the fact that it is even more similar to another well-known
animalcule, _Paramæcium_, than it is to a monad. But _Paramæcium_ is
so huge a creature compared with those hitherto discussed—it reaches
1/120 of an inch or more in length—that there is no difficulty in
making out its organisation in detail; and in proving that it is not
only an animal, but that it is an animal which possesses a somewhat
complicated organisation. For example, the surface layer of its body is
different in structure from the deeper parts. There are two contractile
vacuoles, from each of which radiates a system of vessel-like canals;
and not only is there a conical depression continuous with a tube,
which serve as mouth and gullet, but the food ingested takes a definite
course, and refuse is rejected from a definite region. Nothing is
easier than to feed these animals, and to watch the particles of indigo
or carmine accumulate at the lower end of the gullet. From this they
gradually project, surrounded by a ball of water, which at length
passes with a jerk, oddly simulating a gulp, into the pulpy central
substance of the body, there to circulate up one side and down the
other, until its contents are digested and assimilated. Nevertheless,
this complex animal multiplies by division, as the monad does, and,
like the monad, undergoes conjugation. It stands in the same relation
to _Heteromita_ on the animal side, as _Coleochæte_ does on the plant
side. Start from either, and such an insensible series of gradations
leads to the monad that it is impossible to say at any stage of the
progress—here the line between the animal and the plant must be drawn.
There is reason to think that certain organisms which pass through a
monad stage of existence, such as the _Myxomycetes_, are, at one time
of their lives, dependent upon external sources for their protein
matter, or are animals; and, at another period, manufacture it, or are
plants. And seeing that the whole progress of modern investigation is
in favour of the doctrine of continuity, it is a fair and probable
speculation—though only a speculation—that, as there are some plants
which can manufacture protein out of such apparently intractable
mineral matters as carbonic acid, water, nitrate of ammonia, metallic
and earthy salts; while others need to be supplied with their carbon
and nitrogen in the somewhat less raw form of tartrate of ammonia and
allied compounds; so there may be yet others, as is possibly the case
with the true parasitic plants, which can only manage to put together
materials still better prepared—still more nearly approximated to
protein—until we arrive at such organisms as the _Psorospermiæ_ and the
_Panhistophyton_, which are as much animal as vegetable in structure,
but are animal in their dependence on other organisms for their food.
The singular circumstance observed by Meyer, that the _Torula_ of
yeast, though an indubitable plant, still flourishes most vigorously
when supplied with the complex nitrogenous substance, pepsin; the
probability that the _Peronospora_ is nourished directly by the
protoplasm of the potato-plant; and the wonderful facts which have
recently been brought to light respecting insectivorous plants, all
favour this view; and tend to the conclusion that the difference
between animal and plant is one of degree rather than of kind; and that
the problem whether, in a given case, an organism is an animal or a
plant, may be essentially insoluble.
VIII.
ON CERTAIN ERRORS RESPECTING THE STRUCTURE OF THE HEART
ATTRIBUTED TO ARISTOTLE.
In all the commentaries upon the “Historia Animalium” which I have met
with, Aristotle’s express and repeated statement, that the heart of
man and the largest animals contains only three cavities, is noted as
a remarkable error. Even Cuvier, who had a great advantage over most
of the commentators in his familiarity with the subject of Aristotle’s
description, and whose habitual caution and moderation seem to desert
him when the opportunity of panegyrising the philosopher presents
itself, is betrayed into something like a sneer on this topic.
“Du reste il n’attribue à cet organe que trois cavités,
erreur qui prouve au moins qu’il en avait regardé la
structure.”[36]
To which remark, what follows will, I think, justify the reply, that it
“prouve au moins” that Cuvier had not given ordinary attention, to say
nothing of the careful study which they deserve, to sundry passages in
the first and the third books of the “Historia” which I proceed to lay
before the reader.
For convenience of reference these passages are marked _A_, _B_, _C_,
etc.[37]
Book i. 17.—(_A_) “The heart has three cavities, it lies
above the lung on the division of the windpipe, and has
a fatty and thick membrane where it is united with the
great vein and the aorta. It lies upon the aorta, with
its point down the chest, in all animals that have a
chest. In all, alike in those that have a chest and in
those that have none, the foremost part of it is the
apex. This is often overlooked through the turning upside
down of the dissection. The rounded end of the heart is
uppermost, the pointed end of it is largely fleshy and
thick, and in its cavities there are tendons. In other
animals which have a chest the heart lies in the middle
of the chest; in men, more to the left side, between the
nipples, a little inclined to the left nipple in the
upper part of the chest. The heart is not large, and its
general form is not elongated but rounded, except that
the apex is produced into a point.
(_B_) “It has, as already stated, three cavities, the
largest of them is on the right, the smallest on the
left, the middle-sized one in the middle; they have all,
also the two small ones, passages (τετρημένας) towards
the lung, very evidently as respects one of the cavities.
In the region of the union [with the great vein and the
aorta] the largest cavity is connected with the largest
vein (near which is the mesentery); the middle cavity
with the aorta.
(_C_) “Canals (πόροι) from the heart pass to the lung and
divide in the same fashion as the windpipe does, closely
accompanying those from the windpipe through the whole
lung. The canals from the heart are uppermost.
(_D_) “No canal is common [to the branches of the
windpipe and those of the vein] (οὐδεὶς δ’ ἐστὶ κοινὸς
πόρος) but through those parts of them which are in
contact (τὴν σύναψιν) the air passes in and they [the
πόροι] carry it to the heart.
(_E_) “One of the canals leads to the right cavity, the
other to the left.
(_F_) “Of all the viscera, the heart alone contains blood
[in itself]. The lung contains blood, not in itself but
in the veins, the heart in itself; for in each of the
cavities there is blood; the thinnest is in the middle
cavity.”
Book iii. 3.—(_G_) “Two veins lie in the thorax alongside
the spine, on its inner face; the larger more forwards,
the smaller behind; the larger more to the right, the
smaller, which some call _aorta_ (on account of the
tendinous part of it seen in dead bodies), to the left.
These take their origin from the heart; they pass entire,
preserving the nature of veins, through the other viscera
that they reach; while the heart is rather a part of
them, and more especially of the anterior and larger one,
which is continued into veins above and below, while
between these is the heart.
(_H_) “All hearts contain cavities, but, in those of very
small animals, the largest [cavity] is hardly visible,
those of middling size have another, and the biggest all
three.
(_I_) “The point of the heart is directed forwards, as
was mentioned at first; the largest cavity to the right
and upper side of it, the smallest to the left, and the
middle-sized one between these; both of these are much
smaller than the largest.
(_K_) “They are all connected by passages (συντέτρηνται)
with the lung, but, on account of the smallness of the
canals, this is obscure except in one.
(_L_) “The great vein proceeds from the largest cavity
which lies upwards and to the right; next through the
hollow middle part (διὰ τοῦ κοίλου τοῦ μέσου) it becomes
vein again, this cavity being a part of the vein in which
the blood stagnates.
(_M_) “The aorta [proceeds from] the middle [cavity], but
not in the same way, for it is connected [with the middle
cavity] by a much more narrow tube (σύριγγα).
(_N_) “The [great] vein extends through the heart,
towards the aorta from the heart.
(_O_) “The great vein is membranous like skin, the aorta
narrower than it and very tendinous, and as it extends
towards the head and the lower parts it becomes narrow
and altogether tendinous.
(_P_) “In the first place, a part of the great vein
extends upwards from the heart towards the lung and
the attachment of the aorta, the vein being large and
undivided. It divides into two parts, the one to the
lung, the other to the spine and the lowest vertebra of
the neck.
(_Q_) “The vein which extends to the lung first divides
into two parts for the two halves of it and then extends
alongside each tube (σύριγγα) and each passage (τρῆμα),
the larger beside the larger and the smaller beside the
smaller, so that no part [of the lung] can be found
from which a passage (τρῆμα) and a vein are absent.
The terminations are invisible on account of their
minuteness, but the whole lung appears full of blood. The
canals from the vein lie above the tubes given off from
the windpipe.”
The key to the whole of the foregoing description of the heart lies
in the passages (_G_) and (_L_). They prove that Aristotle, like
Galen, five hundred years afterwards, and like the great majority
of the old Greek anatomists, did not reckon what we call the right
auricle as a constituent of the heart at all, but as a hollow part, or
dilatation, of the “great vein.” Aristotle is careful to state that his
observations were conducted on suffocated animals; and if any one will
lay open the thorax of a dog or a rabbit, which has been killed with
chloroform, in such a manner as to avoid wounding any important vessel,
he will at once see why Aristotle adopted this view.
For, as the subjoined figure (p. 185) shows, the vena cava inferior
(_b_), the right auricle (_R.a._), and the vena cava superior and
innominate vein (_V.I._) distended with blood seem to form one
continuous column, to which the heart is attached as a sort of
appendage. This column is, as Aristotle says, vein above (_a_) and vein
below (_b_), the upper and the lower divisions being connected διὰ
τοῦ κοίλου τοῦ μέσου—or by means of the intervening cavity or chamber
(_R.a._)—which is that which we call the right auricle.
[Illustration:
A dog having been killed by chloroform, enough of the
right wall of the thorax was removed, without any notable
bleeding, to expose the thoracic viscera. A carefully
measured outline sketch of the parts _in situ_ was then
made, and on dissection, twenty-four hours afterwards,
the necessary anatomical details were added. The woodcut
is a faithfully reduced copy of the drawing thus
constructed; and it represents the relations of the heart
and great vessels as Aristotle saw them in a suffocated
animal.
All but the inner lobe of the right lung has been
removed; as well as the right half of the pericardium and
the right walls of the right auricle and ventricle. It
must be remembered that the thin transparent pericardial
membrane appears nothing like so distinct in nature.
_a.b._, Aristotle’s “great vein”; _V.I._, right vena
innominata and vena cava superior; _b_, the inferior
vena cava; _R.a._, the “hollow middle” part of the great
vein or the right auricle; _R.v′_, the prolongation of
the cavity of the right ventricle _R.v_ towards the
pulmonary artery; _tr_, one of the tricuspid valves;
_Pc_, the pericardium; _I.sv_, superior intercostal
vein; _Az_, vena azygos; _P.A._, right pulmonary artery;
_Br_, right bronchus; _L_, inner lobe of the right lung;
_Œ_, œsophagus; _Ao_, descending aorta; _H_, liver, in
section, with hepatic vein, vena portæ, and gall-bladder,
_gb_, separated by the diaphragm, also seen in section,
from the thoracic cavity.]
But when, from the four cavities of the heart recognised by us moderns,
one is excluded, there remain three—which is just what Aristotle says.
The solution of the difficulty is, in fact, as absurdly simple as that
presented by the egg of Columbus; and any error there may be, is not
to be put down to Aristotle, but to that inability to comprehend that
the same fact may be accurately described in different ways, which
is the special characteristic of the commentatorial mind. That the
three cavities mentioned by Aristotle are just those which remain if
the right auricle is omitted, is plain enough from what is said in
(_B_), (_C_), (_E_), (_I_), and (_L_). For, in a suffocated animal,
the “right cavity” which is directly connected with the great vein,
and is obviously the right ventricle, being distended with blood, will
look much larger than the middle cavity, which, since it gives rise
to the aorta, can only be the left ventricle. And this, again, will
appear larger than the thin and collapsed left auricle, which must
be Aristotle’s left cavity, inasmuch as this cavity is said to be
connected by πόροι with the lung. The reason why Aristotle considered
the left auricle to be a part of the heart, while he merged the right
auricle in the great vein, is, obviously, the small relative size of
the venous trunks and their sharper demarcation from the auricle.
Galen, however, perhaps more consistently, regarded the left auricle
also as a mere part of the “arteria venosa.” The canal which leads
from the right cavity of the heart to the lung (or, as Aristotle
puts it (_E_), from the lung to the heart) is, without doubt, the
pulmonary artery. But it may be said that, in this case, Aristotle
contradicts himself, inasmuch as in (_P_) and (_Q_) a vessel, which
is obviously the pulmonary artery, is described as a branch of the
great vein. However, this difficulty also disappears, if we reflect
that, in Aristotle’s way of looking at the matter, the line of
demarcation between the great vein and the heart coincides with the
right auriculo-ventricular aperture; and that, inasmuch as the conical
prolongation of the right ventricle which leads to the pulmonary
artery (_R.v′_ in the Figure), lies close in front of the auricle,
its base may very easily (as the figure shows) be regarded as part of
the general opening of the great vein into the right ventricle. In
fact, it is clear that Aristotle, having failed to notice the valves
of the heart, did not distinguish the part of the right ventricle
from which the pulmonary artery arises (_R.v′_) from the proper trunk
of the artery on the one hand, and from the right auricle (_R.a_) on
the other. Thus the root, as we may call it, of the pulmonary artery
and the right auricle, taken together, are spoken of as the “part of
the great vein which extends upwards” (_P_); and, as the vena azygos
(_Az_) was one branch of this, so the “vein to the lung” was regarded
as another branch of it. But the latter branch, being given off close
to the connection of the great vein with the ventricle, was also
counted as one of the two πόροι by which the “heart” (that is to say
the right ventricle, the left ventricle, and the left auricle of our
nomenclature) communicates with the lung.
The only other difficulty that I observe is connected with (_K_). If
Aristotle intended by this to affirm that the middle cavity (the left
ventricle), like the other two, is directly connected with the lung by
a πόρος, he would be in error. But he has excluded this interpretation
of his words by (_E_), in which the number and relations of the
canals, the existence of which he admits, are distinctly defined. I
can only imagine then, that, so far as this passage applies to the
left ventricle, it merely refers to the indirect communication of that
cavity with the vessels of the lungs, through the left auricle.
On this evidence I submit that there is no escape from the conclusion
that, instead of having committed a gross blunder, Aristotle has given
a description of the heart which, so far as it goes, is remarkably
accurate. He is in error only in regard to the differences which he
imagines to exist between large and small hearts (_H_).
Cuvier (who has been followed by other commentators) ascribes another
error to Aristotle:—
“Aristote suppose que la trachée-artère se prolonge
jusqu’au cœur, et semble croire, en conséquence, que
l’air y pénétre (_l. c._ p. 152).”
Upon what foundation Cuvier rested the first of these two assertions,
I am at a loss to divine. As a matter of fact, it will appear from the
following excerpts that Aristotle gives an account of the structure of
the lungs which is almost as good as that of the heart, and that it
contains nothing about any prolongation of the windpipe to the heart.
“Within the neck lie what is called the œsophagus (so
named on account of its length and its narrowness) and
the windpipe (ἀρτηρία). The position of the windpipe in
all animals that have one, is in front of the œsophagus.
All animals which possess a lung have a windpipe. The
windpipe is of a cartilaginous nature and is exsanguine,
but is surrounded by many little veins....
“It goes downwards towards the middle of the lung, and
then divides for each of the halves of the lung. In all
animals that possess one, the lung is divided into two
parts; but, in those which bring forth their young alive,
the separation is not equally well marked, least of all
in man.
“In oviparous animals, such as birds, and in quadrupeds
which are oviparous, the one half of the lung is widely
separated from the other; so that it appears as if they
had two lungs. And from being single, the windpipe
becomes (divided into) two, which extend to each half of
the lung. It is fastened to the great vein, and to what
is called the aorta. When the windpipe is blown up, the
air passes into the hollow parts of the lung. In these,
are cartilaginous tubes (διαφύσεις) which unite at an
angle; from the tubes passages (τρήματα) traverse the
whole of the lung; they are continually given off, the
smaller from the larger.” (Book i. 16.)
That Aristotle should speak of the lung as a single organ divided into
two halves, and should say that the division is least marked in man,
is puzzling at first; but the statement becomes intelligible, if we
reflect upon the close union of the bronchi, the pulmonary vessels and
the mediastinal walls of the pleuræ, in mammals;[38] and it is quite
true that the lungs are much more obviously distinct from one another
in birds.
Aubert and Wimmer translate the last paragraph of the passage just
cited as follows:—
“Diese haben aber knorpelige Scheidewände, welche unter
spitzen Winkeln zusammentreten, und aus ihnen führen
Oeffnungen durch die ganze Lunge, indem sie sich in immer
kleineren verzweigen.”
But I cannot think that by διαφύσεις and τρήματα, in this passage,
Aristotle meant either “partitions” or openings in the ordinary
sense of the latter word. For, in Book iii. Cap. 3, in describing
the distribution of the “vein which goes to the lung” (the pulmonary
artery), he says that it
“extends alongside each tube (σύριγγα) and each passage
(τρῆμα), the larger beside the larger, and the smaller
beside the smaller; so that no part (of the lung) can be
found from which a passage (τρῆμα) and a vein are absent.”
Moreover, in Book i. 17, he says—
“Canals (πόροι) from the heart pass to the lung and
divide in the same fashion as the windpipe does, closely
accompanying those from the windpipe through the whole
lung.”
And again in Book i. 17—
“It (the lung) is entirely spongy, and alongside of each
tube (σύριγγα) run canals (πόροι) from the great vein.”
On comparing the last three statements with the facts of the case, it
is plain that by σύριγγες, or tubes, Aristotle means the bronchi and so
many of their larger divisions as obviously contain cartilages; and
that by διαφύσεις χονδρώδεις he denotes the same things; and, if this
be so, then the τρήματα must be the smaller bronchial canals, in which
the cartilages disappear.
This view of the structure of the lung is perfectly correct so far
as it extends; and, bearing it in mind, we shall be in a position to
understand what Aristotle thought about the passage of air from the
lungs into the heart. In every part of the lung, he says, in effect,
there is an air tube which is derived from the trachea, and other tubes
which are derived from the πόροι which connect the lung with the heart
(_suprà_, _C_). Their applied walls constitute the thin “synapses” (τὴν
σύναψιν) through which the air passes out of the air tubes into the
πόροι, or blood-vessels, by transudation or diffusion; for there is no
community between the cavities of the air tubes and cavities of the
canals; that is to say, no opening from one into the other (_suprà_,
_D_).
On the words “κοινὸς πόρος” Aubert and Wimmer remark (_l. c._ p. 239),
“Da A. die Ansicht hat die Lungenluft würde dem Herzen zugeführt,
so postulirt er statt vieler kleiner Verbindungen einen grossen
Verbindungsgang zwischen Lunge und Herz.”
But does Aristotle make this assumption? The only evidence so far as
I know in favour of the affirmative answer to this question is the
following passage:—
“Συνήρτεται δὲ καὶ ἡ καρδία τῇ ἀρτηριᾷ πιμελώδεσι
καὶ χονδρώδεσι καὶ ἰνώδεσι δεσμοῖς· ᾗ δὲ συνήρτεται,
κοῖλόν ἐστιν. φυσωμένης δὲ τῆς ἀρτηρίας μὲν ἐνίοις ἐν οὐ
κατάδηλον ποιεῖ, ἐν δὲ τοῖς μείζοσι τῶν ζῴων δῆλον ὅτι
εἰσέρχεται τὸ πνεῦμα εἰς αὐτὴν” (i. cap. 16).
“The heart and the windpipe are connected by fatty and
cartilaginous and fibrous bands; where they are connected
it is hollow. Blowing into the windpipe does not show
clearly in some animals, but in the larger animals it is
clear that the air goes into it.”
Aubert and Wimmer give a somewhat different rendering of this passage:—
“Auch das Herz hängt mit der Luftröhre durch fettreiche,
knorpelige und faserige Bänder zusammen; und da, wo sie
zusammenhängen, ist eine Höhlung. Beim Aufblasen der
Lunge wird es bei manchen Thieren nicht wahrnehmbar, bei
den grösseren aber ist es offenbar, dass die Luft in das
Herz gelangt.”
The sense here turns upon the signification which is to be ascribed to
εἰς αὐτὴν. But if these words refer to the heart, then Aristotle has
distinctly pointed out the road which the air, in his opinion, takes,
namely, through the “synapses” (_D_); and there is no reason that I
can discover to believe that he “postulated” any other and more direct
communication.
With respect to the meaning of κοῖλόν ἐστιν, Aubert and Wimmer observe:—
“Dies scheint wohl die kurze Lungenvene zu sein.
Schneider bezieht dies auf die Vorkammern, allein diese
werden unten als Höhlen des Herzens beschrieben.”