220 THE BIOLOGY OF THE FROG CHAP. 



pancreas be tied so as to destroy the ordinary function of 

 this organ, there is no abnormal production of sugar, and the 

 animal may live for a long time. A large part of the pan- 

 creas may be removed, or the whole organ removed, and a 

 part of it grafted in some other part of the body without 

 producing fatal effects. The animal may also be kept alive, 

 even after complete extirpation of the pancreas, if extracts 

 of this organ are injected into the blood. So long as the 

 body receives substances formed by the pancreas it may be 

 kept alive, but when these are completely withdrawn fatal 

 effects quickly follow. 



In nearly all vertebrate animals there are several organs 

 the function of which was for a long time unknown. Many 

 of them were regarded as rudiments of organs useful once, 

 but now functionless. This was the case with certain small 

 structures such as the thyroid, hypophysis, and adrenal 

 bodies. It is now known that certain of these organs, far 

 from being useless rudiments, are absolutely essential to the 

 maintenance of life. Most of these organs belong in the 

 category of "ductless glands," so called because they have 

 no duct or external outlet. The way in which they function 

 has been a matter of dispute. We know that they act by 

 producing internal secretions which are given off into the 

 blood, and it is held by some that these substances destroy 

 poisons which are produced by the other tissues and which 

 would cause the death of the organism if allowed to accumu- 

 late. Others regard these secretions as affording the 

 stimuli needful to the discharge of the functions of other 

 organs. In certain cases, the latter interpretation seems 

 to be borne out ; but this does not prove that the internal 

 secretions of other organs do not possess antitoxic proper- 

 ties, and in fact there seems to be good evidence, in some 

 instances, that such is the case. 



