PRESIDENTIAL ADDRESS. 635 
adaptations, ¢.e., the reactions of the primitive organism to changes in its environ- 
ment, must become continually more complex, for only by means of increasing 
variety of reaction can the stability of the system be secured within greater 
and greater range of external conditions. The difference between higher and 
lower forms is therefore merely one of complexity of reaction. 
The naked protoplasm of the plasmodium of Myxomycetes, if placed upon a 
piece of wet blotting-paper, will crawl towards an infusion of dead leaves, or 
away from a solution of quinine. It is the same process of adaptation, the 
deciding factor in the struggle for existence, which impels the greatest thinkers 
of our times to spend long years of toil in the invention of the means for the 
offence and defence of their community or for the protection of mankind against 
disease and death. The same law which determines the downward growth 
of the root in plants is responsible for the existence to-day of all the sciences of 
which mankind is proud. 
The difference between higher and lower forms is thus not so much qualitative 
as quantitative. In every case, whatever part of the living world we take as an 
example, we find the same apparent perfection of adaptation. Whereas, how- 
ever, in the lower forms the adaptation is within strictly defined limits, with 
rise in type the range of adaptation steadily increases. Especially is this marked 
if we take those groups which stand, so to speak, at the head of their class. It is 
therefore important to try and find out by a study of various forms the physio- 
logical mechanism or mechanisms which determine the increased range of 
adaptation. By thus studying the physiological factors, which may have made 
for success in the struggle for dominance among the various representatives of 
the living world, we may obtain an insight into the factors which will make for 
success in the further evolution that our race is destined to undergo. 
It is possible that, even at this time, objections may be raised to the applica- 
tion to man of conclusions derived from a study of animals lower in the scale. 
It has indeed been urged, on various grounds, that man is to be regarded as 
exempt from the natural laws which apply to all other living beings. When 
we inquire into the grounds for assuming this anomic, this outlawed condition 
of man, we generally meet with the argument that man creates his own environ- 
ment and cannot therefore be considered to be in any way a product of it. This 
modification or creation of environment is, however, but one of the means of 
adaptation employed by man in common with the whole living kingdom. From 
the first appearance of life on the globe we find that one of the methods adopted 
by organisms for their self-preservation is the production of some artificial 
surroundings which protect them from the buffeting of environmental change. 
What is the mucilaginous envelope produced by micro-organisms in presence of 
an irritant, or the cuticle or shell secreted by the outermost cells of an animal, 
but the creation of such an environment ? All unicellular organisms, as well as 
the units composing the lowest metazoa; are exposed to and have to resist every 
change in concentration and composition of the surrounding water. When, 
however, a body cavity or coelom, filled probably at first with sea-water, made 
_ its appearance, all the inner cells of the organism were withdrawn from the 
distributing influence of variations in the surrounding medium. The coelomic 
fluid is renewed and maintained uniform in composition by the action of the 
organism itself, so that we may speak of it as an environment created by the 
organism. The formation of a body cavity filled with salt solution at once 
increased the range of adaptation of the animals endowed therewith. Thus 
it enabled them to leave the sea, because they carried with them the watery 
environment which was essential for the normal activity of their constituent 
cell units. The assumption of a terrestrial existence on most parts of the earth’s 
surface involved, however, the exposure to greater ranges of temperature than 
was the case in the sea, and indicated the necessity for still further increase 
in the range of adaptation. Every vital process has its optimum tempera- 
ture at which it is carried out rapidly and effectively. At or a little above 
freezing point the chemical processes concerned in life are suspended, so that 
over a wide range of the animal. kingdom there must be an almost complete 
suspension of vital processes during the winter months, and at all times of the 
year a great dependence of the activity of these processes on the surrounding 
