256 



SHINKISHI HATAI 



rat rather than with its body weight and (2) the thymus gland 

 shows an involutionary change manifested by the diminution in 

 its absolute weight after about 85 days in age. These two peculi- 

 arities are both subject to considerable fluctuation which may 

 contribute to the high variability of the thymus in weight. 



In order to give some idea of the degree of variability of this 

 organ as contrasted with others, table 3 is presented. 



TABLE 3 



This table brings out two important facts: (1) The high vari- 

 ability of the thymus, and (2) the fact that the variability is 

 greatest at the period of rapid growth of t-he body and becomes 

 less as the growth of the body is slow^ed. We may attribute 

 the greater variability during the first six weeks to the greater 

 variability of the body weight, since as has been mentioned, the 

 weight of the thymus at this period varies not only with age, but 

 also with the body weight, while in the older rats such is not the 

 case. Finally, in the adult rat we can easily eliminate most of 

 the disturbing factors by careful inspection, inasmuch as these 

 are associated in the main with evid*ent pathological conditions. 



On account of its great variability, nothing can be stated 

 definitely at this moment as to the sex difference in the weight 

 of the thymus gland. So far as our present data are concerned, 

 the thymus gland of the female appears to be slightly hea^vier 

 than that of the male, nevertheless, the difference found is too 

 slight to justify treating the sexes separately, so that the same 

 formulas may be allowed to serve for both. 



