DeEcEMBER I0, 1896] 
NATURE 
P39 
Evolution admits that, as a resut of real causes, characteristics 
may vary and be transmitted to descendants ; hence, species are 
established by transformation from a common origin. Hereditary 
variation and transmission are the two essentials in the concep- 
tion of species as now understood by zoologists and botanists, 
who regard them rather as to what they may become than what 
they are. This new conception of species has brought about an 
entire revolution in the study of biology, it being now recognised 
that individual, or, as it is called, ontogenetic development 
depends on genealogical or philogenetic development, in which 
the causes of existence must be sought. and the explanation found 
of the form presented by animals and plants in the actual state. 
Various theories, which I will briefly note, have been formulated 
to explain the action of the causes which produce the astonishing 
phenomena of variability of character and their hereditary trans- 
mission. The first of these theories, natural selection, which tried 
to explain everything, has had its day, and now is only invoked to 
account for certain secondary characteristics, or those attributed 
to the adaptations of individual forms. In fact to admit, with 
Darwin, the selection of properties subservient to their purpose, 
such as would arise in the struggle for existence, in which the 
strongest would survive, is the same as introducing a teleological 
cause into the explanations of nature, where no struggles nor 
purpose exist, but only phenomena which are in the relation of 
cause to effect, as had been established by natural philosophy. 
The principle of improvement from internal causes, pro- 
pcunded by Nageli, is but the affirmation of a result of which the 
causes, not only internal but also external, acting and reacting on 
each other, still remain to be found. Julius Sachs accepts im- 
provement from internal causes, but adds mechanomcrphosis 
produced in plants by mechanical means, such as the action of 
light and of gravity. 
To study the effects of physico-chemical, or mechanical 
causes in living bodies, Roux has lately formulated his bio- 
mechanical theory, which is far more scientific than the old 
mechanical theory of Descartes. Nevertheless the author does 
not take into account development. which is the fundamental 
principle of evolution, and in consequence of which forms and 
structures cannot all be explained solely by actual causes ; since 
we must not lose sight of the idea that actually existing forms 
are essentially the product of causes which have operated slowly 
and successively in time. Roux, wishing to give the explana- 
tion of the trabecular structure of the liver, and the multipolar 
form of the hepatic cells of adult mammals, refers the cause of 
the orientation of the above-named cells to the action of material 
exchange, and which, from the bipolar form they take in all 
glands, have become transformed into multipolar cells in the 
liver of adult mammals. Hence, he refers also to this cause the 
- transformation into fine network of the nutritive circulation 
which from tubular has become trabecular. But the case given by 
Roux leads us to one conclusion only, namely, that the elements, 
tissues, and organs are so closely correlated, that no alteration 
can take place in one without necessarily occasioning alteration 
in the others. But to know how the liver of adult mammals has 
become trabecular, and its hepatic cells multipolar, it is necessary 
to investigate the history of its genealogical development, such 
a transformation being effected by causes which have worked 
Reed 
in time. ald i a. 
Can this investigation be made? Surely, by not limiting our- 
_ selves to the bare testimony of our senses, but by taking advant- 
_ agealsoof induction. Comparing the liver of the adult with the 
_ liver of the embryo of the same mammals and with the liver 
of the other vertebrates, observation shows that in the embryo 
of mammals the liver is tubular, exactly as it is found in in- 
ferior vertebrates, even in the adult stage ; hence we have been 
able to conclude that there was a period when, in the ancestor 
of the mammals, the liver was tubular through its whole life, 
and that the trabecular form is a later development. Thus far 
it is true we have not pointed out precisely what is the cause, 
or rather what are the causes which have transformed the gland 
from tubular to trabecular ; but can we fill up this hiatus by 
the study of present causes? Inthe example under consideration, 
when we know that the nutritive current runs in one case only 
in one direction, and in the other in various directions, we can- 
“not yet say that we therefore know the cause or causes of such 
variations, since we do not know precisely what were the causes, 
external and internal, which produced the alteration in the 
material exchange. Only by comparative research of organic 
forms we find that the trabecular form of the mammals is derived 
from the tubular form, and we thus come toan important result, 
| NO. 1415, VOL. 55] 
thanks to which we can establish the parentage of animals— 
namely, that in the embryo are registered the genealogical 
documents of the race of his ancestors; and if we can but read 
them we shall find them, although more or less modified. 
Usually the more recent are the more clearly imprinted, while 
it is difficult to decipher the very old ones; indeed, sometimes 
these are entirely lost. We have an example in the develop- 
ment of the Molgulide and of the Salpze, which, together with 
the Ascidians and other forms, constitute the class Tunicata. 
The larvae of the Ascidians pass through two phases of 
development ; in the first, they present the cordate type, which 
subsequently disappears, being transformed in the second phase 
into the definite and exact type of the Tunicata. Now, in the 
Molgulidze and in the Salpe the first phase is suppressed ; the 
cordate type is not repeated, and development commences 
directly from the Tunicata type. Without the Ascidians we 
should be unable to establish the relationship of the Tunicata 
with 4mphioxus and the Vertebrates; and the class Tunicata 
would have remained where at one time it was placed, between 
worms and molluscs. Now, thanks to historical and philogenetic 
research, we know that a high place awaits the Tunicata beside 
the Cordata and the Vertebrates ; and we are led to admit that 
these three great classes have a common origin, the Proto- 
cordatus, which has disappeared, but which we can reconstruct 
from the characteristics we meet with in these three classes. 
The reconstruction of extinct organisms, which we are able to 
effect by the study of morphology, demonstrates the highest 
function of this science ; the veracity of such reconstructions has 
been sometimes confirmed by successive zoological and 
palzeontological discoveries. From the fundamental characteristics 
we meet with in the embryos of Ascidians, Amphzoxus and the 
Vertebrata, we can affirm with certainty that the common 
progenitor of the Tunicata, the Cordata and the Vertebrata, had 
the form of a fish; possessed an intestine divided into an 
anterior part chiefly respiratory, and a posterior part digestive ; 
had a body divided into segments, a spinal cord, and a nervous 
dorsal tube decurrent from its anterior to its posterior extremity, 
an arterial longitudinal dorsal vessel and a venous ventral one. 
Here, then, is one of the important results achieved by science 
through the study of organic forms. 
Nor have results of lesser importance been obtained by re- 
searches on heredity. Progressing by experiment; aided by 
optical appliances, which in our day have made astounding 
progress, and by which the microscope has been raised to a high 
pitch of perfection ; furnished with the most precise and delicate 
methods of modern histological technique, by which every living 
element can be detected in the various phases of its activity ; we 
have succeeded in discovering an important part of the secrets 
with whic® nature has surrounded the generation of living beings, 
secrets which naturalists of time not long past had declared 
impenetrable. 
Guided by experimental methods, we may hope that science 
will be able ere long to solve complex and important questions 
relating to the organisation of living bodies ; we seek not the 
nature of things, which is impossible for us to learn, but the true 
reason of phenomena, remembering what the Lincei had affirmed 
from their very first institution—liberty of conscience, love of 
truth, confession of ignorance. 
THE NATURAL IMMUNITY OF VENOMOUS 
SNAKES ; 
IN a previous article (NATURE. October 24, 1895, p. 621) 
the ‘‘Serum Treatment of Snake-bite” was briefly dis- 
cussed by the writer of this note ; and Calmette’s and Fraser’s 
researches are now so well known, that it is not necessary to 
give a summary of them. One or two points, however, must 
again be alluded to, because recently Dr. D. Cunningham, of 
Calcutta,! has carried on some important experiments which 
throw fresh light on the matter, and which also supply answers 
to some of the questions raised by the writer in the above- 
mentioned article. 
The most surprising conclusion of Calmette and Fraser was that 
the serum of an animal immunised against cobra poison will 
protect not only against this poison, but also against the poisons 
of other snakes. It might be thought that this is an argument 
against Behring’s law that the action of immunising serum Is 
1 “Scientific Memoirs by Medical Officers of the Army of India,” 1895, ix. 
p- 1-30. 
