GROWTH AFFECTED BY FEEDING DUCTLESS GLANDS 301 



of young guinea pigs was accelerated by injections of extract 

 of calf pineals. Pineal substance hastened sexual development 

 in guinea pigs. Males were more susceptible than females to 

 pineal treatment. The treated animals did not grow larger 

 than normal adults and their growth was apparently propor- 

 tional in all parts of the body. The 'sexual precocity' noted 

 by McCord perhaps can be explained by the fact that in grow- 

 ing animals the sexual development normally tends to keep pace 

 with somatic growth. In stunted animals sexual maturity is 

 retarded as seen in inanition experiments (Jackson '15); con- 

 versely it is to be expected that a hastened somatic growth is 

 accompanied by a corresponding development of the reproduc- 

 tive organs. This condition can hardly be called sexual pre- 

 cocity, especially if the sex organs are not relatively over- 

 developed. 



Dandy ('15) was able to remove the pineal body from young 

 dogs with no apparent after-effects. 



Many experimental data that have been published are worth 

 very little to us because of incomplete records and also because 

 animals of one strain kept under certain conditions have been 

 used as control animals and checked against experimental ani- 

 mals of a possibly different strain kept perhaps under different 

 conditions. It is also true that in many experiments, although 

 all the animals are of the same strain and are kept under similar 

 conditions, only a small number are used and these represent 

 different litters. Since it has been shown by Jackson ('13) and 

 King ('15) that in albino rats variability in body weight within 

 a litter is only about half as great as general racial variability, 

 the advantage of taking controls and experimental animals 

 from the same litter is obvious. The apparent 'results' obtained 

 in many experiments may very well be due merely to the above- 

 mentioned factors and not to the experiment itself. 



III. MATERIAL AND METHODS 



The albino rat (Mus norvegicus albinus) was selected for the 

 experiment because it is a convenient form for use and more is 

 known about the growth of this animal than of any other, ow- 

 ing to the work of Donaldson, Hatai, Jackson, Slonaker, Lowrey, 



