Transcriber’s note: Table of Contents added by Transcriber.
CONTENTS
Preventive Inoculation 115
Professor Ewart's Penycuik Experiments 126
Colonies and the Mother Country 139
The Future of the Negro in the Southern States 147
The Physical Geography of the Lands 157
The New York Botanical Garden 171
Gas and Gas Meters 179
The Sun's Destination 191
A Biographical Sketch of an Infant 197
Correspondence 206
Scientific Literature 213
The Progress of Science 219
THE
POPULAR SCIENCE
MONTHLY
EDITED BY
J. McKEEN CATTELL
VOL. LVII
MAY TO OCTOBER, 1900
NEW YORK AND LONDON
McCLURE, PHILLIPS AND COMPANY
1900
COPYRIGHT, 1900,
BY McCLURE, PHILLIPS AND COMPANY.
[Illustration: PROFESSOR WOLCOTT GIBBS,
PRESIDENT OF THE NATIONAL ACADEMY OF SCIENCES, EMERITUS RUMFORD
PROFESSOR AND LECTURER ON THE APPLICATIONS OF SCIENCE TO THE USEFUL
ARTS AT HARVARD UNIVERSITY.]
THE
POPULAR SCIENCE
MONTHLY.
JUNE, 1900.
PREVENTIVE INOCULATION. (I.)
BY DR. W. M. HAFFKINE.
DIRECTOR-IN-CHIEF, GOVERNMENT PLAGUE RESEARCH LABORATORY, BOMBAY.
It was due to certain particularly favorable circumstances that the
first ideas on preventive inoculation were gathered from observations
on smallpox patients. Such circumstances were presumably the following:
_a._ It is a disease which attacks epidemically, in a short time and
within a small area, large numbers of people, thus permitting of easy
comparisons and suggesting conclusions from the facts observed.
_b._ Its fatality is comparatively small, so that after each outbreak a
large number of convalescent persons remain alive to serve as objects
for future observation and comparison.
_c._ These convalescents are marked and are thus easily distinguishable
from the rest of the population who have not been attacked, and even
the severity of the disease they have gone through is, so to say,
written down on their faces and bodies.
_d._ The disease is easily communicable, owing to the infectious matter
appearing on the surface of the patient’s body in the pustules.
It was easy, therefore, to notice in this case, as was indeed very
early done in the East, that a person who has gone through one attack,
as shown by his pitted face, very rarely suffers even during severe
subsequent epidemics. Smallpox, like other epidemic diseases, breaks
out in some years in very fatal, in others in milder forms. It is
admissible that by a mixed process of thought and faith an impression
insensibly gained ground that it was _lucky_ to have been touched by
the smallpox deity--of course, not in years when that deity appeared in
terrifying mortality. Accordingly, in times of _mild_ outbreaks people
would not be very careful in avoiding infected persons, and would even
seek their company so as to get infected from them. The practice of
intentionally rubbing one’s skin with a pustule, or with bits of it,
from an attacked person, must have been a subsequent stage.
Such or a similarly gradual development of ideas may explain why
it is impossible to fix a date or place for this discovery, which
indeed goes back to the darkness of antiquity. Research points to
its practice among the Chinese and Hindus in very ancient times. The
Chinamen induced a mild attack by inserting a crust from a smallpox
pustule into the nostrils. The Hindus, on the contrary, used the fluid
pus, which they inoculated under the skin of the arm. In either case,
in the course of a week, the inoculated was attacked by some slight
preliminary symptoms followed by an eruption, sometimes profuse,
sometimes scanty, and then the disease would run its ordinary course.
The only difference between an attack caused by inoculation and that
caused by natural infection was, as a rule, the milder nature of the
former, especially when the matter for inoculation was taken from a
notoriously mild case. The result, however, was by no means certain.
A mild form of an infectious disease may be due either to the virus
being of a weak nature; and then such a virus would be the desired
one for inoculating persons seeking artificial protection; or else
the mildness of the case may be due to the patient himself being of a
resistant organization, in which case, though exhibiting mild symptoms
himself, he may be harboring an intense form of contagion, apt to cause
a severe outbreak when transferred to other less resistant persons.
Many plans were consequently adopted to secure with more certainty a
mild artificial infection. Some of these were directed to the treatment
of the patient preparatory to inoculation, others to the preparation
of the infectious matter in order to attenuate its virulence. The
Brahmans, who were the operators in India, in addition to selecting
material from patients with a mild form of the disease, were accustomed
not to employ the pus at once, but to keep it wrapped up in cotton wool
for a period of about twelve months, and thus to weaken its power. They
inoculated in the early part of the year, at the time when smallpox
prevailed, and the practice they used was to moisten with water a bit
of cotton wool prepared in the previous outbreak, to place it on the
arm of the person to be inoculated, and to prick the arm, through the
wool, over an area of about the size of a twenty-five cent piece. In a
few days a vesicle would appear at the seat of the inoculation, which
later on developed into a pustule and eruption. Notwithstanding these
precautions, great variation in the results was observed, and many
succumbed to the operation; but those that passed through it safely
were proof against further attacks.
Besides the personal risk to the inoculated, the illness produced
in them was infectious to others, and unprotected persons coming in
contact with the inoculated were likely to get infected from them.
The latter result was largely avoided by the practice adopted by the
Brahmans of inoculating all the inhabitants of a family or village at
the same time. The benefits secured under the above precautions were
considered far to outweigh the risks of inoculation.
With the extension of smallpox westward the system of artificial
protection spread toward Europe through the intermediary of travelers
and merchants. The Arabs and Turks appreciated its benefits at an
early date. The slave dealers supplying the bazaars and harems of
Constantinople adopted the system to protect against disfigurement
their Circassian and other live stock. In the early part of the
eighteenth century the method was made known to the English
practitioners by Lady Mary Wortley Montagu, the wife of the English
ambassador at Constantinople, who had her two children inoculated
according to the Turkish system. Curiously enough, it was soon
afterward discovered that a similar method was in practice among
the peasants of some of the districts in Wales and the Highlands of
Scotland, and had long been known there as ‘buying the smallpox.’ When
inoculation was given a more extensive trial it was found, in England
as in the East, that the effect of it was decidedly beneficial, but
fraught with danger. At first one in every fifty of those operated
upon succumbed to the consequences of inoculation. By improved methods
the mortality was gradually reduced to one in a thousand; but the most
serious danger lay in the spread of infection to healthy persons. The
precaution of inoculating whole groups of inhabitants at one time, or
of keeping the inoculated apart from the healthy, as had been practiced
by the Brahmans ages ago, was overlooked, and the result was often
disastrous to the community.
* * * * *
It was at this time that Jenner achieved great progress and threw a
vast amount of new light on the question. As is well known, he started
from a belief that existed in the west of England, that cowpox was a
bovine form of smallpox, and that the milkers who attended on cows
suffering from that disease and who became infected with the eruptions
on the teats and udders, passed through a mild illness, which rendered
them immune against smallpox. Jenner determined to put this tradition
to the test, and succeeded in establishing, by a few accurate and
well-planned experiments, a series of most important facts.
He showed, first, that cowpox could be artificially given to the cow by
infecting it with virus from a smallpox patient, and that the disease
thus produced was transferable by inoculation from cow to cow.
He showed further, that by having been bred in the tissues of the
cow, the virus lost its intense infective properties for man. When
the matter from an artificially infected animal was transferred by
inoculation to a human being, it produced at the seat of its insertion
a discrete vesicle, which was not followed by a general eruption, as
would often be the case with the original smallpox virus.
Though the illness thus induced was not infectious in the sense that it
would not be communicated spontaneously from person to person, it could
be so transferred artificially by inoculating patients with the lymph
from a ripe human vesicle.
When transferred from cow to cow or from man to man the matter
preserved unchanged the same property of producing the mild inoculation
vesicle, harmless to the patient and to his surroundings; and thus a
matter for inoculation was obtained of _invariable strength_, what was
called later on, by Pasteur, ‘virus fixe.’
The last and the most essential property which Jenner demonstrated to
belong to the substance in question was the following: A man who had
been inoculated with that substance could afterward be with impunity
infected with a virus taken direct from a smallpox patient; the
inoculation would be either abortive altogether or the effect much
milder than in a man not so prepared. Jenner concluded from this most
striking result that the inoculation with the matter cultivated by
him in the cow would protect a man forever against contamination with
smallpox, and he called that matter ‘vaccine,’ or cow lymph.
Jenner’s experiments produced an immense impression throughout the
world, and inoculation according to his system, which was called
‘vaccination,’ was rapidly applied to large numbers of people. When
outbreaks of smallpox occurred in the midst of vaccinated communities,
observations began to come in as to the actual effectiveness of the
method in protecting against the disease.
These observations proved that the system possessed an undoubted
and exceedingly high beneficial effect, though the following two
restrictions had to be imposed upon the originally conceived
expectations:
1. The protection was not absolute. In every outbreak of smallpox a
number of patients were and are met with who are attacked, generally
mildly, but also in some cases fatally, though they had undergone a
successful vaccination, some even at a comparatively recent date before
the attack. Only the proportion of such patients to the whole of the
vaccinated community is very markedly smaller than the proportion of
attacks in the non-vaccinated; and also the severity of the attack, as
well as the proportion of deaths to attacks, is in the vaccinated much
smaller.
2. This favorable difference between the outbreaks among vaccinated and
non-vaccinated is maintained not for life, but for a limited number of
years, and disappears gradually, and at length altogether, unless the
individuals be revaccinated. Observation has shown that the period
during which the protective effect of vaccination lasts extends over
from three to seven years.
Vaccination very rapidly displaced inoculation, and spread to every
part of the civilized world. The results have been dwelt upon in
innumerable books and pamphlets. At present great outbreaks of smallpox
have become very rare, at least in the civilized part of the world, and
there is a tendency to forget or ignore the devastations they used to
cause.
* * * * *
The first successful attempt in extending the system of inoculation
to other diseases was made only after the discovery of the fact that
‘infection’ is caused by living animal or vegetable parasites, capable
in the majority of cases of being cultivated and bred in artificial
media outside the animal body. Pasteur found that he was able to effect
protection against disease similar to vaccination against smallpox by
the use of such artificially bred micro-organisms.
It may be interesting to relate that this important discovery was
made unintentionally, and represents one of those happy ‘accidents’
which occur to those who diligently search. Pasteur had been working
with cultures of chicken-cholera microbes, an extremely fatal form
of virus when it is introduced into fowls and small birds. It so
happened that one of his cultures was left forgotten in the incubator
when work was stopped for the vacation. On the return of Pasteur and
his assistants the experiments were continued. When the bottle was
discovered, thinking that the microbes might have been exhausted or
dead from long starvation, Pasteur tried to make what is called a
fresh culture of them, by inseminating a sample from the old bottle
into a freshly prepared nutritious broth. The microbes were not dead,
and multiplied and grew luxuriantly; but when they were injected into
a fowl they caused only a transient and non-fatal disease. To make a
fresh start, Pasteur took some old blood, which he had drawn a long
time previously from a chicken-cholera fowl and preserved in a cupboard
in the laboratory in a sealed-up tube, and made a culture with the
material that was in that tube. The culture thus obtained killed
fresh fowls as usual, but when it was injected into the bird that had
resisted the first culture it resisted this injection also. Pasteur,
who excelled all men I ever knew in his ability of quickly analyzing
and discerning true connections between facts, required no further
hints. Others might perhaps have dwelt on the peculiarity of the fowl
that happened to resist the injections, or on some other circumstances.
Pasteur relinquished this and other suggestions at once, and thought
of the microbe. The fact that old specimens of microbes may become
impotent when injected into animals was known to him, and was readily
explained by the vitality of such microbes being lowered or exhausted
by starvation. But, then, such a microbe when transferred into a fresh
medium, if not dead, generally regains its vigor, and after that, when
inoculated into an animal, it produces its usual effect. The remarkable
circumstance about the culture left in the incubator was that even when
it was transferred into a fresh medium and its vitality renewed, it
remained still impotent. Pasteur concluded from this that an infectious
microbe possesses two distinct properties: one, which it shares with
any other living being--viz., _vitality_--which may be weakened or
strengthened according to the conditions of life and food; and another,
which he considered as its ‘virulence,’ its power of causing diseases,
which may be also weakened or strengthened by special means, but which
is quite independent of ‘vitality.’
The lucidity of thought of which Pasteur made proof on this occasion
was magnificent. Later researches confirmed and explained these facts
with a singular completeness, and now the idea, as is always the case,
looks simple and self-evident. One must remember that at that time
Pasteur had every reason to believe that disease is caused by the
mere fact of a foreign micro-organism of a given species penetrating
and settling down to live in the system of a man or animal. Its
capability of _living_ there, _i. e._, its vital properties, seemed
all that was necessary for causing disease. It was only later that
it was found that pathogenic microbes cause diseases by producing
so-called toxines or poisonous substances distinct from their own
bodies and separable from them. The process may be illustrated by a
comparison, for instance, with a cobra or any other animal producing
a special venom. By starvation or some other treatment the vitality
of the cobra may be temporarily weakened. When it obtains fresh food
again and gets generally in good condition, it recovers, without its
ability of producing venom having been in any way impaired. On the
other hand, a snake may be by an operation deprived of its fangs and
power of secreting poison without its health and strength being in the
least affected. Pasteur at once asserted that in a similar way it was
possible by starvation to weaken a breed of microbes without their
virulence being diminished, and, on the other hand, to deprive them
of their power of producing disease without impairing their vitality,
though what the above power consisted in he did not know. He called
the latter result _attenuation_ of a virus. An attenuated virus in his
meaning is therefore a special breed of pathogenic microbes which can
be maintained, by suitable breeding, in best conditions of health, but
which has lost either partially or entirely its power of producing
poison and disease.
Pasteur extracted from the few experiments related above a further
most-important conclusion--viz., that such an attenuation was due to
and could be produced artificially by the effect of oxidation. This
he deduced from the fact that the microbes in the sealed-up tube had
not lost their virulence, while those forgotten in the open bottle in
the incubator and exposed to the access of air had done so. Oxidation
proved indeed to be one of the most general methods of artificially
producing attenuated virus, to which method later on were added
others--the effect of light, of chemicals, of passage through certain
animals, etc.
And, of course, the last and crowning conclusion was that an ordinary,
susceptible fowl that has undergone the injection with an attenuated
culture becomes immune against a culture which kills other fowls; and
that conclusion, in the particular circumstances under which Pasteur
was working, proved to be true.
Pursuing the new line of research, Pasteur demonstrated that a
protection similar to that obtained against smallpox and chicken
cholera could be secured also against _anthrax_, a disease which, by
the destruction it caused among sheep and cattle, was entailing heavy
loss on the farmers of France. After a long series of experiments
he prepared two specimens of virus, different in strength, but both
weaker than the natural contagion, and worked out the proportions in
which sheep, horses and cows could be safely injected first with the
weakest virus and then with the virus of the somewhat greater strength,
after which they became capable of withstanding the strongest anthrax
infection.
In honor of Jenner, who was the first to discover the way of preparing
a virus of a fixed strength safe to be used for the preventive
treatment of men, Pasteur proposed that all such artificially bred,
so to say, domesticated forms of microbes be called _vaccines_, while
the word _virus_ be reserved for a contagion growing in nature in
a natural condition, or taken direct from an infected individual.
The French distinguish between ‘vaccin,’ which is used as a generic
term in Pasteur’s sense, and ‘vaccine,’ which name they reserve for
smallpox vaccinia lymph. The word ‘vaccination’ has been also extended
to designate inoculation with artificially vaccinized virus, while
the word ‘inoculation’ is used for the injection of a natural, not
vaccinated virus, taken direct from a patient. The latter distinction
is, however, not yet strictly maintained in English literature, nor in
the subsequent pages of this paper.
Pasteur gave a memorable demonstration of the efficiency of his
method of anthrax vaccination. At Pouilly-le-Fort, in the midst of
an assemblage of scientists, delegates of agricultural societies,
government officials, landlords, farmers and representatives of the
press, he performed the following experiment: Sixty sheep were taken;
ten of these were put aside, twenty-five were vaccinated with the
two attenuated anthrax vaccines at an interval of twelve days, and
twenty-five were left untouched. Twelve days afterward the two groups
of twenty-five sheep were inoculated with virulent anthrax; and the
result was that at the next visit the twenty-five unvaccinated and one
vaccinated pregnant female were found dead, while twenty-four out
of the twenty-five that had been vaccinated were perfectly well, and
exhibited during the whole time they were kept under observation the
same degree of health as the ten sheep that had been put aside for
comparison.
* * * * *
An impetus was given by these discoveries to researches having for
their object the protection of _men_ against infectious diseases. The
most important of these researches was Pasteur’s own into the nature
of hydrophobia and rabies, and the way of inoculating against that
disease. This was followed a few years later by the preparation of a
prophylactic against cholera.
Inoculation against hydrophobia was rendered possible by the discovery
of the fact that the rabies or hydrophobia virus is found in a pure
condition, free from other microbes, in the nervous centers of animals.
The material for inoculation is prepared from such nervous matter, the
virulence of which is rendered _fixe_, as will be mentioned below.
The cholera microbe, which was subsequently named _comma bacillus_,
was discovered by Koch in 1883, in the intestinal contents of cholera
patients. Two years later cholera broke out in Spain, and Dr. James
Ferran, a Spanish physician, began inoculating men with living cultures
of comma bacillus taken from patients attacked with the disease. The
procedure in its essential features corresponded to the pre-Jenner
method of inoculation. The failure to fix the strength of the virus
used for treatment rendered the method subject to the same uncertainty
as that which was connected with inoculation with smallpox virus taken
direct from patients. It was impossible to predict the effect of the
injections. Comma bacilli taken from cholera patients may, under
cultivation, show themselves extremely virulent, or, on the contrary,
extremely mild. There are specimens which, when injected into a Guinea
pig, even in an insignificant dose, will prove fatal to it, and there
are others which will appear harmless when given in a dose seventy
times greater. The immediate effect, and the protection caused by the
inoculation, must, of course, vary accordingly. The attempt made by
Ferran caused great interest, and a number of scientific commissions
were sent to Spain from different countries of Europe to study the
results of his work. They could, however, come to no conclusion, and
the treatment speedily lost its position. Only some seven years later
a method was found of fixing the strength of the cholera virus. I was
connected with this stage of the work, and it may perhaps present some
interest to the reader to relate the way in which the problem was
solved, and to show how gradual is the development of ideas by which
results in laboratory investigation are arrived at.
It has been mentioned already that the virulence of microbes changes
under the influence of different agents in Nature--heat, light,
chemicals. When a virus is first obtained from a patient or outside a
patient its preceding history, its antecedents, the conditions under
which it lived before, are extremely variable. Jenner’s method of
cultivating the smallpox virus by transferring it from calf to calf
secured for that virus uniform conditions of life, and its strength
could thus be maintained unchanged for an indefinite length of time.
Pasteur, in the preparation of hydrophobia vaccine, followed the same
plan, and found in the successive inoculation from rabbit to rabbit a
method of propagating the hydrophobia virus in a uniform condition.
But attempts made to cultivate in a similar way the comma bacillus by
transferring it from animal to animal failed.
The most susceptible animals for the cholera microbe are Guinea pigs.
There are two principal methods of ingrafting upon them the virus:
Koch’s method of administering it through the mouth and leaving it to
develop in the intestines of the animal, and Pfeiffer’s of injecting
it, not into the intestines, but into the abdominal or peritoneal
cavity, where the intestines are lodged, by introducing there the virus
with a hypodermic needle not allowed to penetrate into the intestines
themselves. But by neither of these methods could the microbe be
cultivated in an unbroken series of animals, as it became gradually
weakened and soon lost its power of affecting such animals. For the
purpose in question, cultivation in the peritoneal cavity had the
advantage that in a healthy individual the peritoneum is free from
other microbes, whereas in the intestines there are always present a
large number of micro-organisms which interfere in variable ways with
the growth of the particular microbes.
But when one inoculates the peritoneal cavity of a Guinea pig with a
dose of cholera microbes sufficient to cause a fatal disease, it is
found, when the animal dies, that the microbes have died also. Thus,
the attempt to ingraft the virus from a first animal to a subsequent
one is checked at the very beginning. This initial difficulty was
overcome by merely giving to the first animal a dose larger than was
necessary to cause a fatal effect. The animal then succumbs more
rapidly, and the microbes have no time to disappear. At the post-mortem
examination there is found, in the peritoneal cavity, a small amount of
exudate liquid which contains large numbers of those microbes alive.
When, however, that exudate is injected into the peritoneal cavity of a
second animal that animal does not succumb to the infection, or even if
it succumbs one finds that the microbes have again disappeared in this
second animal. By starting with, a still larger initial dose one may
have three, perhaps four, successive animals affected by the virus, but
it invariably ends by being weakened, and finally dies out.
In trying to obviate this result I found, perhaps contrary to
expectations, that the exudation liquid should be exposed to the air
for a few hours before it is injected into a subsequent animal. This
result was contradictory to the effect which Pasteur had found to be
exercised by atmospheric oxygen on the virulence of microbes, and
it requires at least some provisional explanation. The microbes of
cholera differ from a certain number of other microbes in that they
stand in need of a free and abundant access of air for growing and
multiplying quite satisfactorily. They are deprived of this condition
in the peritoneal cavity of an animal. It is possible, therefore,
that a certain opposition between the maintenance or development of
virulence on the one hand, and a lowering in vitality on the other,
takes place while they are cultivated there, and a respite must be
given them between each successive ‘passage’ through the Guinea pig by
leaving them for a time in the free atmosphere. Be that explanation
true or not, the result is that under such conditions the successive
animals inoculated with the virus do succumb, and even in a shorter
and shorter time, after the inoculation, the microbe apparently
undergoing under such a treatment a progressive increase in virulence.
A similar development up to a certain stage was observed by Pasteur
when transferring the rabies virus from rabbit to rabbit. The last
difficulty that presented itself was the following: The exudation
liquid which is found in the peritoneal cavity post mortem varies in
quantity; sometimes it is inconveniently large and diluted; sometimes,
on the contrary, so scanty that it becomes difficult to collect and
transfer it to another animal. I found that this variation stands in
connection with the size of the animal, so that a diluted exudation
fluid can be concentrated by injecting it into a small animal, while a
too much concentrated exudate is rendered more dilute by transferring
it to an animal of a larger size.
Thus, by the initial use of more than a fatal dose, by alternating
cultivation in an animal with exposure to air, and by attention to
the size of the animal employed, a material was obtained which, as
mentioned, increased in intensity from the first and proved fatal to
animals in a shorter and shorter time after inoculation. Later the
virus reached a stage when it killed a Guinea pig of three hundred
and fifty grammes weight in eight hours. After that, in each further
inoculation the time of eight hours remained stationary, showing
that the virus has reached the condition of a ‘virus fixe.’ These
experiments were conducted by me in the Pasteur Institute, in 1889 to
1893, simultaneously on the cholera microbe and on the bacillus of
typhoid. The two exhibited a number of common features in their nature,
and the results as above detailed for the cholera microbe were found
valid for the typhoid bacillus also.
Starting from the ‘virus fixe’ obtained as above, a method of double
inoculation was worked out, one with an attenuated virus prepared
from the ‘virus fixe,’ and another with the latter itself. The two
‘vaccines,’ when inoculated successively into Guinea pigs, protected
them against all possible forms of cholera infection. The vaccines
were cultivated on a solid medium, and when the crop of microbes was
ready at the end of some twenty-four hours, they were washed off the
surface of the medium and used as a kind of medicinal plant. It was
found that the substances contained in the microbes preserved to a
great extent their immunizing properties even when the microbes were
killed by some delicate processes not affecting considerably their
chemical constitution. The washings could, therefore, be prepared
in dilute solutions of carbolic acid, and employed in the form of
preserved vaccines. In 1892 and in the beginning of 1893 I made a
series of experiments in Paris, in Netley, in London, in Cambridge,
and in Calcutta, with these carbolized cholera vaccines, which had
been preserved in sealed tubes for a period of six to seven months,
and it was possible to show the protective effect of the method on
animals as conclusively as Pasteur had done in the demonstration at
Pouilly-le-Fort with anthrax. For the inoculation in man, however, I
decided to use at first only unaltered living vaccines, as much more
promising than the dead ones, especially from the point of view of the
durability of the effect.
[_To be concluded._]
PROFESSOR EWART’S PENYCUIK EXPERIMENTS.[A]
[A] Abstract from an article in the Quarterly Review discussing
Professor Ewart’s ‘Experimental Investigations on
Telegony,’ read before the Royal Society last year, and his
book, ‘The Penycuik Experiments,’ published by Messrs. A. &
D. Black.
The views and works of Darwin have influenced in an unexpected way
the nature of the work carried on by biological investigators during
the latter end of this fast-dying century. To a great extent, while
generally holding the doctrines he held, they have forsaken his methods
of inquiry.
If animals and plants have arrived at their present state by descent
with modification from simpler forms, it ought to be possible by
careful searching to trace the line of ancestry; and it is this
fascinating but frequently futile pursuit which has dominated the
minds of many of our ablest zoölogists for the last thirty years. To
such an extent has this pedigree hunting been carried that there is
scarcely a group of invertebrates from which the vertebrates have
not been theoretically derived; and to-day one of the ablest of our
physiologists is using his great powers in the attempt to trace the
origin of the backboned animals from a spiderlike creature, and is
exercising his ingenuity in a plausible but unconvincing effort to
equate the organs of a king-crab with those of a lamprey. This appeal
to comparative anatomy and the consequent neglect of living animals
and their habits are no doubt partly due to the influence of Huxley,
Darwin’s most brilliant follower and exponent. He had the engineer’s
way of looking at the world, and his influence was paramount in many
schools. The trend which biology has taken since Darwin’s time is also
partly due to a fervent belief in the recapitulation theory, according
to which an animal in developing from the egg passes through phases
which resemble certain stages in the past history of the ancestors of
the animal. For example, there is no doubt that both birds and mammals
are descended from some fishlike animal that lived in the water and
breathed by gills borne on slits in the gullet, and every bird and
mammal passes through a stage in which these gill-slits are present,
though their function is lost and they soon close up and disappear. In
the hope, which has been but partially realized, that a knowledge of
the stages through which an animal passes on its path from the ovum to
the adult would throw light on the origin of the race, the attention
of zoölogists has been largely concentrated on details of embryology,
and a mass of facts has already been accumulated which threatens to
overwhelm the worker.
The two chief factors which play a part in the origin of species are
heredity and variation, and until we know more about the laws which
govern these factors we can not hope to arrive at any satisfactory
criteria by which we can estimate the importance of the data
accumulated for us by comparative anatomists and embryologists. Signs
are not wanting that this view is beginning to be appreciated. The
publication of ‘Materials for the Study of Variation,’ by Mr. Bateson,
a few years ago, shows that there exists a small but active school of
workers in this field; and the recent congress on hybridization, held
in London under the auspices of the Royal Horticultural Society, is
evidence that in America, on the Continent and in Great Britain one of
the most important sides of heredity is being minutely and extensively
explored. Prof. Cossar Ewart’s experiments, which we shall attempt to
summarize, deal with heredity and cognate matters, and, although they
are so far from complete that the results hitherto obtained can not be
regarded as final, they mark an important stage in the history of the
subject.
Five years ago Professor Ewart began to collect material for the study
of the embryology of the horse, about which, owing to the costliness of
the necessary investigations, very little is at present known. At the
same time he determined to inquire into certain theories of heredity
which have for centuries influenced the breeders of horses and cattle,
and the belief in which has played a large part in the production of
our more highly bred domestic animals. Foremost among these is the
view widely held among breeders that a sire influences all the later
progeny of a dam which has once produced a foal to him. This belief in
the ‘infection of the germ,’ or ‘throwing-back’ to a previous sire, is
probably an old one--possibly as old as the similar faith in maternal
impressions which led Jacob to place peeled wands before the cattle
and sheep of his father-in-law Laban. The phenomenon has recently
been endowed with a new name--Telegony. Since the publication of Lord
Morton’s letter to Dr. W. H. Wollaston, President of the Royal Society,
in 1820, it has attracted the attention not only of practical breeders,
but of theoretical men of science. The supporters of telegony, when
pressed by opponents, having almost always fallen back on Lord Morton’s
mare, it will be well to recall the chief incidents in the history of
this classic animal.
It appears that early in this century Lord Morton was desirous of
domesticating the quagga. He succeeded in obtaining a male, but,
failing to procure a female, he put him to a young chestnut mare, of
seven eighths Arab blood, which had never been bred from before. The
result was the production of a female hybrid apparently intermediate
in character between the sire and the dam. A short time afterward Lord
Morton sold his mare to Sir Gore Ouseley, who bred from her by a fine
black Arabian horse. The offspring of this union, which were examined
by Lord Morton, were a two-year-old filly and a year-old colt. He
describes them as having “the character of the Arabian breed as
decidedly as can be expected where fifteen sixteenths of the blood are
Arabian, and they are fine specimens of that breed; but both in their
color and in the hair of their manes they have a striking resemblance
to the quagga.” The description of the stripes visible on their coats
is careful and circumstantial, but the evidence of the nature of the
mane is less convincing: “Both their manes are black; that of the filly
is short, stiff, and stands upright, and Sir Gore Ouseley’s stud groom
alleged that it never was otherwise. That of the colt is long, but so
stiff as to arch upward and to hang clear of the sides of the neck, in
which circumstance it resembles that of the hybrid.”
This is the classical, we might almost say the test, case of telegony:
the offspring resembled not so much the sire as an earlier mate of
the dam. The facts related tended to confirm the popular view, and
that view is widely spread. Arab breeders act on the belief, and it is
so strongly implanted in the minds of certain English breeders that
they make a point of mating their mares first with stallions having
a good pedigree, so that their subsequent progeny may benefit by its
influence, even though poorly bred sires are subsequently resorted to.
The evidence of Lord Morton’s mare convinced Darwin of the existence
of telegony; after a careful review of the case he says “there can
be no doubt that the quagga affected the character of the offspring
subsequently got by the black Arabian horse.” Darwin, however, latterly
came to the conclusion that telegony only occurred rarely, and some
years before his death expressed the opinion that it was “a very
occasional phenomenon.” Agassiz believed in telegony. He was strongly
of the opinion “that the act of fecundation is not an act which is
limited in its effects, but that it is an act which affects the whole
system, the sexual system especially; and in the sexual system the
ovary to be impregnated hereafter is so modified by the first act that
later impregnations do not efface that first impression.”
Romanes also believed that telegony occasionally occurred. He paid a
good deal of attention to the matter, commenced experiments in the hope
of settling the question, and corresponded at length on this subject
with professional and amateur breeders and fanciers. The result of his
investigations led him to the conclusion “that the phenomenon is of
much less frequent occurrence than is generally supposed. Indeed, it is
so rare that I doubt whether it takes place in more than one or two per
cent of cases.” A recent controversy in the Contemporary Review shows
us that Mr. Herbert Spencer is a firm upholder of telegony, and that he
has a theory of his own as to the mode in which it is brought about. He
suggests that some ‘germ-plasm’ passes from the embryo into the mother
and becomes a permanent part of her body, and that this is diffused
throughout her whole structure until it affects, among other organs,
the reproductive glands. This view, which in some respects recalls
the pangenesis of Darwin, is intermediate between the saturation and
the infection hypothesis. Professor Ewart refers to it as indirect
infection.
Weismann, to whom we owe the term telegony, came to consider the facts
for and against its existence in connection with his well-known inquiry
into the inheritance of acquired characters. If telegony be true, there
is no need to look further for a clear case of the inheritance of a
character which has been acquired during the lifetime of the parent.
The quagga-ness--if one may be permitted to use such an expression--of
Lord Morton’s mare was acquired when she was put to the quagga or
shortly afterward, and was transmitted to her foals. A clearer case of
a character acquired during lifetime and transmitted to offspring could
not be imagined. Weismann does not absolutely deny the possibility of
the existence of telegony, but he would like more evidence. In the
Contemporary Review he writes, “I must say that to this day, and in
spite of the additional cases brought forward by Spencer and Romanes, I
do not consider that telegony has been proved.” And further: “I should
accept a case like that of Lord Morton’s mare as satisfactory evidence
if it were quite certainly beyond doubt. But that is by no means the
case, as Settegast has abundantly proved.” He would, in fact, refer the
case to reversion, and quotes Settegast to the effect that every horse
breeder is well aware that the cases are not rare when colts are born
with stripes which recall the markings of a quagga or zebra. We shall
return to this point later.
A considerable number of German breeders support the contention of
Weismann that telegony is as yet unproved, and it may be pointed out
that in Germany, on the whole, breeders have had a more scientific
education than in England, and that in that country science is
regarded with less aversion or contempt than is usually the case among
so-called practical men in England. We may mention one more case of an
experienced breeder who was equally skeptical--the late Sir Everett
Millais, who was, as is well known, an authority of great weight in the
matter of dog-breeding. He writes as follows, in a lecture entitled
Two Problems of Reproduction: “I may further adduce the fact that in a
breeding experience of nearly thirty years’ standing, during which I
have made all sorts of experiments with pure-blood dams and wild sires,
and returned them afterward to pure sires of their own breeds, I have
never seen a case of telegony, nor has my breeding stock suffered. I
may further adduce the fact that I have made over fifty experiments
for Professor Romanes to induce a case of telegony in a variety of
animals--dogs, ducks, hens, pigeons, etc.--but I have hopelessly
failed, as has every single experimenter who has tried to produce the
phenomenon.”
It is thus evident that there is a considerable body of opinion,
both practical and theoretical, for and against telegony; and
that a reinvestigation of the subject is urgently needed. Such a
reinvestigation has been begun by Professor Ewart at Penycuik. Since
the clearest and most definite evidence of this throwing back to a
previous sire is derived from the crossing of different species of the
_Equidae_, it was desirable to repeat the experiment of Lord Morton.
This is now unfortunately impossible, because the quagga is extinct.
The zebra is, however, still with us, and the mating of a zebra
stallion with every variety of horse, pony, and ass, and subsequently
putting the dam to pure-bred sires, has been the more important part of
the numerous experiments carried on in the Midlothian village some ten
miles southwest of Edinburgh.
[Illustration: MATOPO.]
Before considering in detail the result of the experiments it will be
necessary to say a few words on the question of the various species of
zebra; and since, like Weismann, Professor Ewart explains certain of
the phenomena attributed to telegony by reversion, it will be as well
to inquire how far reversion is known among the _Equidae_, and what
evidence we have that the ancestor of the horse was striped.
Matopo, the zebra stallion from which Professor Ewart had up to last
midsummer bred eleven zebra-hybrids from mares of various breeds and
sizes, belongs to the widely distributed group of Burchell’s zebras.
Many subspecies or varieties are included in this group, which, as
regards the pattern of the stripes, passes--in certain varieties found
in Nyassaland--into the second species, the mountain zebra, once
common in South Africa. The third species is the Grévy’s zebra of Shoa
and Somaliland; it is probably this species which attracted so much
attention in the Roman amphitheaters during the third century of our
era. A pair of Somali zebras has recently been presented to the queen
by the Emperor Menelik, and is now lodged in the Zoological Gardens,
Regent’s Park. The species measures about fifteen hands high, is
profusely striped, and stands well apart from the other two groups. It
is important to note that, in Professor Ewart’s opinion, it is the most
primitive of all the existing striped horses.
There is no direct evidence that the ancestors of horses were striped.
Certain observers think that some of the scratches on the lifelike
etchings on bone, left us by our palæolithic cave-dwelling ancestors,
indicate such stripes, but little reliance can be placed on this. On
the other hand, there is much indirect evidence. Every one who has
an eye for a horse, and who has traveled in Norway, is sure to have
noticed the stripings, often quite conspicuous, on the dun-colored
Norwegian ponies. Colonel Poole assured Darwin that the Kattiawar
horses had frequently “stripes on the cheeks and sides of the nose.”
Breeders are well aware that foals are often born with stripes,
usually on the shoulders or legs, less frequently on the face. Such
stripes, as a rule, disappear as the colt grows up, but can often be
detected in later life for a short time after the coat has been shed;
they are sometimes only visible in certain lights, and then produce
somewhat the same impression as a watered silk. From the facts that
more or less striped horses are found all over the Old World; that in
Mexico and other parts of America the descendants of horses which were
introduced by the Spaniards and which afterward ran wild are frequently
dun-colored and show stripes; that foals are frequently striped; and
that mules not uncommonly have leg and shoulder stripes, the inference
is largely justified that the ancestors of all our horses were striped.
We now pass to the experiments made at Penycuik in crossing the zebra
Matopo with various mares of different breeds: 1. Matopo was first
mated with Mulatto, one of Lord Arthur Cecil’s black West Highland
ponies. The result was the hybrid Romulus (see p. 132), which on the
whole, both in mental disposition and bodily form, takes more after his
father than his mother. His striping is even more marked than that of
his sire. He has a semi-erect mane which has been shed annually. The
pattern of the markings, on both body and face, resembles the stripes
on a Somali zebra--which, as we have seen, is regarded by Professor
Ewart as the most primitive type--more than they resemble that of any
of Burchell’s zebras. The profuse striping is a point of difference
between this hybrid and Lord Morton’s. The quagga-hybrid was less
striped than many dun-colored horses.
The mother Mulatto was next mated with a highly bred gray Arab horse,
Benazrek. The offspring agrees in all respects with ordinary foals;
it had, however, a certain number of indistinct stripes, which could
only be detected in certain lights. The stripes were not nearly so
clear as in a foal bred by Mr. Darwin from a cross-bred bay mare and a
thoroughbred, and they disappeared entirely in about five months.
[Illustration: ROMULUS, TWENTY-SEVEN DAYS OLD.]
Recently Mulatto has produced a third foal to Loch Corrie, a sire
belonging to the Isle of Rum group of West Highland ponies, and closely
resembling his mate. This foal was about as much striped as its
immediate predecessor. In both cases the pattern of the stripe differed
not only from that of Matopo, the previous sire, but from that of the
hybrid Romulus. These two foals seem to lend some support to telegony;
but the evidence which might be drawn from the second of them is
destroyed by the fact that the sire Loch Corrie has produced foals from
two West Highland mares, one brown and one black, and each of these
foals has as many and as well marked stripes as the foal of Mulatto.