ORGANIC REGULATION 95 



short exposures, come into play during prolonged ex- 

 posureto a diminished oxygen concentration. Another 

 striking instance of the same class of fact is in con- 

 nection with the effects, referred to in the previous 

 lecture, of repeated bleeding or transfusion of blood, 

 as observed by Boycott and Douglas. After repeated 

 bleedings the animal replaces the lost blood with 

 increasing rapidity. After repeated transfusions it 

 gets rid of the excess with corresponding readiness. 

 Presumably in the one case there is an increase in 

 the amount or activity of the blood-forming tissues, 

 and in the other an increase of the blood-destroying 

 tissues. 



We have only to look round, outside the limits of 

 the present conventional physiology, in order to find 

 innumerable instances of similar facts. Striking ex- 

 amples are afforded by the phenomena of immunity 

 to attacks by micro-organisms, and to the action of 

 poisons. Still more remarkable instances are those 

 connected with the recovery of function or reproduc- 

 tion of tissue after injury or disease, or even complete 

 loss of parts of the body. In the higher organisms 

 reproduction of lost parts is a less prominent feature 

 than in lower organisms, but indirect restoration of 

 function is a fact of common observation, and is in 

 some ways more significant and remarkable. 



It thus appears that with disturbance of external or 

 internal environment, or living structure, the reactions 

 which occur are, whether immediate or gradual, of such 

 a character that the organism adapts itself so as to 

 maintain, not merely its existence as a structure, but 



