PHENOMENA OF LIFE 25 



thyroid is followed by death. It was discovered some time ago 

 that this gland might be removed with impunity if a piece of a 

 healthy gland from another animal, such as a sheep, were grafted 

 under the skin in any part of the body. The foreign piece of 

 tissue appropriates a blood supply and becomes functional in its 

 new position. This is one of the many cases proving that a 

 definite positional relation of organs is not always necessary if 

 their secretions are present. 



The opponents of vitalism have also brought forward many 

 arguments against that theory from a study of enzymes or fer- 

 ments, a class of substances which cause chemical reactions with- 

 out undergoing any change themselves. An example is ptyalin, 

 which is present in human saliva and has for its function the 

 change of starch to sugar. A large number of substances of this 

 sort are known to be present in living organisms. The explana- 

 tion of their actions makes clear many processes which were 

 formerly supposed to be due to certain vitalistic principles. Re- 

 search in this field is only in its infancy. 



These instances are sufficient to show that the mechanistic 

 point of view is a much more progressive one than the vitalis- 

 tic. Through its influence scientists have been able to prove 

 that a large number of the activities present in living matter are 

 subject to definite laws, many of which have been known for a 

 long time to physicists and chemists. However, this method has 

 not explained all vital phenomena, and perhaps never will. 



