198 THE AMERICAN NATURALIST. 
It is without the purpose of this paper to discuss the causes 
which are responsible for the production of venous abnormal- 
ities. It seems fair to assume, however, that any cause which 
may disturb the character of the normal stimuli that control 
the development of an organism may correspondingly influence 
the veins, by either arresting, accelerating, or even annulling 
their development. 
Such causes, the effects of which undoubtedly influence 
these normal stimuli, must be numerous, and among others 
the following might be mentioned: Domestication, inbreeding, 
disease, drugs, and shock. 
It seems, therefore, reasonable to assume that breeding 
experiments, carried out on these lines, might give us some 
clue as to the direct causes, as well as the relation of cause 
and effect, which are responsible for the production of abnor- 
malities of the vascular system. 
PRINCETON, N. J., January, 1900. 
