THE ANIMALS STUDIED AND THE TECHOTC 



artery which enters it is examined and com- 

 pared with the blood in the vein which leaves 

 it. Certain substances are found in the latter 

 which are not present in the former and which 

 are also found in the gland itself. These sub- 

 stances, therefore, are regarded as internal se- 

 cretions of the organ. Attempts are made to 

 isolate these substances in the chemical labora- 

 tory and to discover their nature and composi- 

 tion. They are injected into another animal 

 to observe what effect they have upon its bodily 

 functions. Another operation is done at which 

 the organ or part of the organ is removed, and 

 the effects of its removal upon the animal econ- 

 omy is observed. If the removal of the organ 

 results in profound disturbances, its internal 

 secretion, secured from another animal, is fed 

 or injected and the results carefully noted. 

 Good results being secured an attempt is 

 made to transplant from another animal the 

 whole or a part of the organ in question in or- 

 der to see if it is possible to restore to an ani- 

 mal, affected with damage or loss of this organ 

 by disease, the secretion which is necessary for 

 its economy. The laboratories of the physiolo- 

 gists who carry on such studies are equipped 

 with the most exact instruments for determin- 



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