348 THEORETICAL BIOLOGY 



excitation by individuals, appears with especial clearness in 

 the white blood-corpuscles, which move about freely through 

 the tissues of the body, collecting together at the stimulated 

 parts, in order to efface there the injuries that produced the 

 stimulus. 



Recently it has been shown that a whole network of 

 excitation-transference by individuals runs through the body, 

 'and plays a very important part there, especially in the 

 digestive processes. " Hormone " is the name given to these 

 substances, which are cast into the blood-stream by certain 

 cells of the alimentary canal ; they form a special stimulus 

 for certain other digestive glands, which thereupon pour 

 out their secretion into the gut. For the most part, this 

 chemical transference of excitation accompanies the nervous 

 one, but it remains quite independent thereof. 



Further, it has been shown that there are a whole number 

 of internal glands, the secretion of which, cast into the blood- 

 stream, affects other cells as a stimulus, and activates them. 



Finally, the whole taking up of food by the cells from 

 the blood-stream and the body-fluids must be referred to 

 stimulation of individuals and the action that ensues. 



To the same class of facts belongs the power the tissues 

 have of reacting to poisons by throwing anti-bodies into the 

 blood-stream. But in this the protoplasm seems to play a 

 part, and the direction itself seems to come in. 



The action of vitamins on the tissues also points to an 

 " individual " reaction, the omission of which has harmful 

 consequences. 



Although this field of investigation is still very obscure, 

 and we are dependent on vague conjecture, especially as to 

 the stimuli that accelerate or restrict cell-multiplication, we 

 shall not go far wrong if, instead of trying to solve these 

 newly-discovered relations by referring them to simple 

 mechanical or chemical processes, we rely on the transfer- 



