ON THE WEIGHT OF THE THYMUS GLAND OF THE 

 ALBINO RAT (MUS NORVEGICUS ALBINUS) 

 ACCORDING TO AGE 



SHINKISHI HATAI 



The Wialar Tnslilute of Anatomy and Biology 



ONE CHART 



In my recent paper ''On the weight of the abdominal and tho- 

 racic viscera, ductless glands and eyeballs of the albino rat (Mus 

 norvegicus albinus) according to body weight" (Hatai '13), it was 

 not possible to make any statement concerning the thymus gland 

 because its weight is correlated with age rather than with body 

 weight, and the data from rats of known ages were inadequate. 



During the last few months, however, these data for the thy- 

 mus have been collected and the following study is now pre- 

 sented as supplementary to the one cited above. 



The investigation has been based mainly on the data obtained 

 by Dr. Jackson from a colony of rats kept at the University of 

 Missouri (Jackson '13). Jackson's records, however, were lim- 

 ited to seven age periods only: birth, 7 days, 20 days, 6 weeks, 

 10 weeks, 5 months and 1 year. Thus in order to determine the 

 period of the maximum weight of the thymus, as well as to fill 

 the various intervals not filled by him, I have made numerous 

 observations on the Albinos from the colony kept at The Wistar 

 Institute. The Wistar rats, however, were not used until I had 

 tested with data obtained from them the weight of the thymus 

 at the age periods already given by Jackson and found that the 

 two sets of determinations agreed satisfactorily. 



I take this opportunity to acknowledge my indebtedness to 

 Professor Jackson, who has granted me the free use of his entire 

 collection of data on the weight of the thymus gland. 



The total number of rats used for this investigation was 229 

 males (165 Jackson and 64 Wistar) and 207 females (179 Jackson 



251 



THE AMERICAN JOr nNAI. OF ANATOMY, VOl,. If), NO. 2 



