350 EXPERIMENTAL GIGANTISM 



following considerations. If earthworms are a complete diet for 

 salamanders, the worm-fed animals should grow at the maximum rate 

 characteristic of the species, provided that the calories and vitamines 

 are in sufhcient quantity to make the maximum rate of growth at that 

 particular temperature possible. If by chance the anterior lobe should 

 have a higher food value than the earthworm, this could not result 

 in a better growth as long as the food value of the earthworm suffices 

 for the maximum normal growth. If the anterior lobe of the hypophy- 

 sis contains only ordinary food substances and no specific hormone 

 for growth, the rate of growth of the animal should not exceed the spe- 

 cific maximum rate. 



Hence only two conditions had to be provided for. First, all ani- 

 mals, controls and experimental, had to be kept at the same tempera- 

 ture, a condition which was carefully provided for. Second, all ani- 

 mals were given as much food as they desired to take. This condi- 

 tion was approached as nearly as possible. 



The worm-fed animals took the worms readily and voluntarily. 

 The gland-fed animals, however, had to be fed by pushing the pieces 

 of gland into their mouths; yet it was possible to adjust the quantity 

 of food according to the appetite of the animals. They yield readily 

 if the food is gently pressed against their jaws, and swallow the food 

 quickly when they are hungry; while they push the food back by means 

 of the tongue or eject it when it is forced into the mouth, if they are 

 not hungry. 



The quantity of food taken up by the controls was generally greater 

 than the quantity of hypophysis taken by the experimental animals. 



Characteristics of Growth of Normal Salamanders. 



Two species of salamanders were employed in these experiments, 

 Amhy stoma opacum and Amhystoma tigrinum. Since little is known 

 about the normal growth of these animals, some data pertaining to 

 it may be recorded here. 



Large numbers of Amhystoma opacum were reared from eggs in my 

 laboratory and the growth of the species has been recorded over long 

 periods. The longest record I possess is that of four animals which 

 at present are 3 years (161 weeks) of age and were raised from eggs of 



