32 president's address. 



constitutes the variation. In smooth oi' hairy varieties We do hot postulate 

 an individual development of hairs subjected one by one to selection and 

 survival or repression. 



Disease. — The study of the physiology of unhealthy, injured, or 

 diseased organisms is called pathology. It necessarily has an immense 

 area of observation and is of transcending interest to mankind who do 

 not accept their diseases unresistingly and die as animals do, so purifying 

 their race, but incessantly combat and fight disease, producing new and 

 terrible forms of it, by their wilful interference with the earlier rule of 

 Nature. 



Our knowledge of disease has been enormously advanced in the last 

 quarter of a century, and in <an important degree our power of arresting 

 it, by two great lines of study going on side by side and originated, not 

 by medical men nor physiologists in the narrow technical sense, but 

 by naturalists, a botanist, and a zoologist. Ferdinand Cohn, Professor of 

 Botany in Breslau, by his own researches and by personal training in his 

 laboratory, gave to Robert Koch the start on his distinguished career 

 as a bacteriologist. It is to Metschnikoff the zoologist and embryologist 

 that we owe the doctrine of phagocytosis and the consequent theory of 

 immunity now so widely accepted. 



We must not forget that in this same period much of the immortal work 



of Pasteur on hydrophobia, of Behring and Jloux on diphtheria, and 



of Ehrlich and many others to whom the eternal gratitude of mankind is 



due, has been going on. It is only some fifteen years since Calmette 



showed that if cobra poison were introduced into the blood of a horse in 



less quantity than would cause death, the horse would tolerate with little 



disturbance after ten days a full dose, and then day after day an 



increasing dose, until the horse without any inconvenience received an 



injection of cobra poison large enough to kill thirty horses of its size. 



Some of the horse's blood being now withdrawn was found to contain a 



very active antidote to cobra poison — what is called an antitoxin. The 



procedure and preparation of the antitoxin is practically the same as 



that previously adopted by Behring in the preparation of the antitoxin 



of diphtheria poison. Animals treated with injections of these antitoxins 



are immune to the poison itself when subsequently injected with it, or, 



if already suffering from the poison (as, for instance, by snake-bite), are 



readily shown by experiment to be rapidly cured by the injection of the 



appropriate antitoxin. This is, as all will admit, an intensely interesting 



bit of biology. The explanation of the formation of the antitoxin in the 



blood and its mode of antagonising the poison is not easy. It seems that 



the antitoxin is undoubtedly formed from the corresponding toxin or 



poison, and that the antagonism can be best understood as a chemical 



■ reaction by which the complex molecule of the poison is upset, or effectively 



modified. 



The remarkable development of Metschnikoff's doctrine of phago- 

 cytosis during the past quarter of a century is certainly one of the 



