562 
ought to find their home with nerve-cells governing the blood- 
vessels, take up with nerve-cells governing the dilator structures 
of the pupil. 
And if we turn to other nerves, greater aberrations are 
found. We have seen that the nerves running from the central 
nervous system to involuntary structures may be divided into 
two sets: the sympathetic nerves on the one hand, and the 
cranial and sacral nerves on the other. An important cranial 
nerve is the vagus ; it causes, when in action, cessation of the 
heart-beat, contraction of the cesophagus, contraction or inhi- 
bition of the stomach, and various other effects. It does not 
send nerve-fibres to any of those structures of the head which 
we have seen the sympathetic ganglion at the top of the neck 
—the superior cervical ganglion—so liberally supplies. And 
yet the vagus nerve, if it has a proper opportunity of growing 
into the superior cervical ganglion, will do so, and there 
establish connections with the nerve-cells. Thus the nerve 
which properly exercises control over certain viscera in the 
thorax and abdomen is capable of exercising control over 
structures in the head, such as the iris, the blood-vessels and 
the glands. The details of the process, with which I will not 
trouble you, do not afford any clear evidence that the nerve- 
fibres of the vagus pick and choose amongst the nerve-cells of 
the superior cervical ganglion ; the fibres appear rather to form 
their terminal branches around any kind of nerve-cell, so that, 
in fact, the action which the nerve-fibre will in future bring 
about depends, not on any intrinsic character of its own, but upon 
the nature of the action carried on by the nerve-cell. The 
nerve-cell may cause secretion from a gland, or contraction of a 
blood-vessel, or dilation of the pupil, or movement of hairs ; 
whichever action it causes, the nerve-fibre which joins it from the 
vagus nerve can cause for the future, and it can cause no other, 
In this case, then, we arrive at results which are hopelessly at 
variance with the view that the nerve-fibres and nerve-cells of 
the involuntary nervous system are divided into classes which 
are fundamentally different. In other words, that theory which 
is spoken of as the theory of specific nerve-energy does not 
apply here. 
But if this is so, how are we to account for the selective 
power shown by the sympathetic nerve-fibres which I have men- 
tioned earlier? That the different classes of nerve-fibres and 
nerve-cells with which we are dealing have not those deep and 
inherent differences which are required by the theory of specific 
nerve-energy is, it seems to me, certain. Nevertheless, there 
may be some differences of a comparatively superficial nature 
which suffice to explain the selective activity observed. We 
may suppose that a re-growing nerve-fibre will in favourable cir- 
cumstances join a nerve-cell the function of which is the same 
as that of its original cell, but that if there are hindrances in the 
way of this return to normal action, and if the conditions are 
favourable for joining a nerve-cell acting on some other tissue, 
why then it will join this. It is as if it had a preference, but 
did not care overmuch. We might perhaps express the facts by 
saying that there are different varieties of pre-ganglionic fibres, 
but no species. 
We have been speaking so far of the nerve-fibres which run 
from the brain and spinal cord to the peripheral nerve-cells. 
The nerve-fibres which run from the peripheral nerve-cells have 
also, there is reason to believe, a large measure of indifference 
as to the kind of work they perform. The limits of this in- 
difference have yet to be investigated. 
I have said earlier that in mammalia nerve-fibres are not 
known to run to connective-tissue cells or to epidermic cells. 
But in some lower vertebrates certain connective-tissue cells are 
under the control of the central nervous system. Thus in the 
frog the pigmented connective-tissue cells, which play a large 
part in determining the colour of the skin, can be made to con- 
tract or to rearrange their pigment granules—and so change the 
colour of the skin—by excitation of certain nerves. In all 
probability, the motor nerve-fibres to the pigment-cells belong 
to the same class as the nerve-fibres which run to the arteries 
and to the glands—z.e. they belong to the autonomic system. 
We have seen that unstriated muscle-cells and gland-cells in 
different parts of the body are by no means equally supplied 
with motor nerve-fibres, and it may be that in mammals there 
are certain connective-tissue cells which receive motor nerve- 
fibres. Further, if it is true, as it well may be, that nerve-fibres 
which run toa gland are capable in favourable conditions of 
making connections with a blood-vessel, it is not beyond hope 
NO. 1562, VOL. 60] 
LAL IE OW aga 
[OcToBER 5, 1899 
that either kind of nerve-fibre may experimentally, by offering 
it favourable conditions, be induced to join connective-tissue 
cells. 
The factors which determine whether a particular tissue or 
part of a tissue is eventually supplied with nerve-endings, and 
the degree of development of these, are the factors which deter- 
mine evolution in general. In the individual, it is exercise of 
function which leads to the development of particular parts ; in 
the race, itis the utility of this development which leads to their 
preservation. And so it is conceivable that in some lower 
vertebrate at some time, the autonomic nervous system may have 
developed especially in connection with those tissues which 
appear in ourselves to be wholly unprovided with motor nerve- 
fibres. 
I am tempted, before ending, to make a slight digression. 
Those who have occasion to enter into the depths of what is 
oddly, if generously, called the literature of a scientific subject, 
alone know the difficulty of emerging with an unsoured dis- 
position. The multitudinous facts presented by each corner of 
nature form in large part the scientific man’s burden to-day, and 
restrict him more and more, willy-nilly, to a narrower and 
narrower specialism. But that is not the whole of his burden. 
Much that he is forced to read consists of records of defective 
experiments, confused statement of results, wearisome descrip- 
tion of detail, and unnecessarily protracted discussion of un- 
necessary hypotheses. The publication of such matter is a 
serious injury to the man of science; it absorbs the scanty 
funds of his libraries, and steals away his poor hours of leisure. 
Here I bring my remarks to a close. I have endeavoured 
to give as clearly as possible what seem to me to be the con- 
clusions which logically follow from certain data, but I would 
not have you believe that I regard them as representing more 
than the immediate point of view. As the wise man said : 
“‘Hardly do we guess aright at things that are upon earth, and 
with labour do we find the things that are before us.” 
AMERICAN ASSOCIATION FOR THE 
ADVANCEMENT OF SCIENCE. 
THE presidential addresses delivered before the Sections of 
Zoology and Botany of the American Association, by 
Profs. S. H. Gageand C. R. Barnes, respectively, are printed in 
Scéence of September 8. The subjects were ‘‘ The Importance 
and the Promise in the Study of Domestic Animals” and ‘* The 
Progress and Problems of Plant Physiology” and the subjoined 
extracts show some of the points dealt with. Abstracts of 
several other sectional addresses have already appeared in 
NATURE, p. 515. 
Prof. Gage described a few ways in which the study of do- 
mestic animals has thrown light on the problems confronting 
mankind in his social ideals, in preventive medicine, in physi- 
ology and hygiene, in embryology and comparative anatomy and 
in the doctrine of the evolution of organic forms. He showed 
that, with the higher forms at least, that is the forms most 
closely related to man, and with whose destiny his own eco- 
nomic, hygienic and social relations are most closely interwoven, 
the domestic animals have in the past and promise in the future 
to serve the best purpose because of the abundance of the 
material in quite widely separated groups of animals which long 
have been and still are under greatly differing conditions and 
surroundings ; and, finally, because this material is plentiful and 
under control, and thus may be studied throughout the entire 
life cycle. 
There has been and still is too great a tendency in biology to 
study forms remote and inaccessible. This is, perhaps, partly 
due to the fascination of the unknown and the distant, and 
the natural depreciation of what is at hand. But study of 
these supposedly generalised types has proved more or less 
disappointing. No forms now living are truly primitive and 
generalised throughout. They may be in parts, but in parts 
only. The stress of countless ages has compelled them to adjust 
themselves to their changing environment, to specialise in some 
directions so far that the clue through them to the truly primi- 
tive type is very much tangled or often wholly lost. Indeed, 
every group is in some features primitive. 
As any complete study requires much material at all stages 
the higher forms must be of the domesticated groups, or wild 
