90 ORGANISM AND ENVIRONMENT 
ganic or organic substances. The organs, such as the 
liver, or fat-containing tissues, in which material is 
stored, appear to behave similarly; and we have now 
every reason to believe that we should find the same 
regulating activity in every organ or part of the body 
if our methods of investigation were sufficiently deli- 
cate, and we knew the small differences to be detected. 
In every direction the progress of physiology and 
pathology is revealing the astounding delicacy and 
complication of the regulating processes. 
Up to a certain point we can rest satisfied in the 
idea that the regulation of the internal medium de- 
pends upon the specific structures and corresponding 
reactions of the organs which bring about the regula- 
tion. But the more we learn about the delicacy and 
complexity of the regulating processes, the more defi- 
nitely does a difficulty appear. It is not for nothing 
that the body regulates its internal environment so 
exactly. The investigations which reveal the exacti- 
tude of the regulation reveal equally its fundamental 
importance to the nutrition and normal working of 
every part of the body. The organs and tissues which | 
regulate the internal environment are themselves . 
centres of nutritional activity, dependent from moment - 
to moment on their environment. They are constantly-' 
taking up and giving off material of many sorts, and | 
their “structure” is nothing but the appearance taken 
by this flow of material through them. The fact has 
already been referred to that when the supply of 
oxygen to the tissues is seriously restricted the result 
is not merely a slowing down of activity, but actual 
