ORGANIC REGULATION 95 
short exposures, come into play during prolonged ex- 
posure to 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 
