GROWTH AFFECTED BY FEEDING DUCTLESS GLANDS 341 



body as a whole and in the various organs and parts. Several 

 minor differences are to be noted, but all are perhaps within the 

 limit of normal variability. The testes, kidneys (male), ovaries, 

 and suprarenals show a decrease in weight which is of doubtful 

 significance, as (except in the case of the ovaries) it is not con- 

 stant in every litter. My results agree with Priore ('15) who 

 obtained negative results on body growth by injection of pineal 

 extracts. They disagree, however, with those of Dana and 

 Berkeley ('14) and McCord ('14, '15) who obtained an accelera- 

 tion in body growth by feeding pineal substance. 



V. CONCLUSIONS 



Some of the principal results of the present investigation may 

 be summed up briefly as follows: 



1. The normal growth of the albino rat varies materially, 

 not only in different 'strains' and under different conditions of 

 environment, but even among litters when all conditions are 

 as nearly constant as possible. It is therefore not sufficient to 

 rely upon the established norms of growth for comparison, but 

 in all cases experimental and control animals should be selected 

 of the same sex and from the same litter or litters. 



2. In the case of rats with unusually rapid (or slow) growth, 

 in addition to comparison with (older or younger) rats of cor- 

 responding size and weight, due regard for possible changes 

 correlated with age must be observed. Such changes have 

 previously been noted in the water content of nervous system 

 (Donaldson), weight of the thymus (Hatai), and probably the 

 weight of the eyeballs (Jackson). Indications of similar age- 

 changes (independent of body weight) are found in the skeleton, 

 liver, kidneys, heart and spleen. Compared with animals of 

 the usual age at a given bod}^ weight, the skeleton seems to be 

 relatively heavy in older animals, and the other organs are ap- 

 parently heavier in younger rapidly growing animals. 



3. There is apparently no sexual difference in the relative 

 weight of the pineal body, such as has been found in the supra- 

 renal glands (Jackson '13, Hatai '13) and the hypophysis (Hatai 

 '13). 



