EFFECTS OF THIRST ALBINO RATS 457 



age groups, one to four weeks and five to thirteen weeks. All 

 four groups show a marked apparent increase in weight, which is 

 about 60 per cent in all except the younger group of females 

 (37.7 per cent). This difference is not on account of the appear- 

 ance of the normal sex difference, however, for normally the supra- 

 renals become larger in the female. As a matter of fact, the tend- 

 ency to sexual difference in weight does not appear in these thirst 

 experiments, (contrary to the observations of Jackon) ('15 a) in 

 underfeeding). 



In the rats underfed beginning at three weeks of age Jackson 

 ('15 a) found an apparent increase of 12 to 39 per cent in the 

 weight of the suprarenals. A much smaller increase (5 per cent) 

 was found by Stewart (19) in underfed newborn rats. 



In adult rats during thirst there is a relatively small loss in 

 weight of the suprarenal glands (Kudo, '21). 



HYPOPHYSIS 



The hypophysis in rats above 50 grams in body weight must be 

 considered separately in the sexes, since it then normally becomes 

 relatively heavier in the female. This does not affect my con- 

 trols (grouped together in table 2) , and it is evident from table 2 

 that there likewise appears no sexual differentiation in weight in 

 the test rats during the thirst experiments (in agreement with the 

 inanition experiments of Jackson, '15 a). There is evidently 

 no significant change in the average weight of the hypophysis in 

 the one to four weeks' group, but a marked increase (37.5 to 

 43.8 per cent) in the five to thirteen weeks' group. 



Jackson ('15 a) found a smaller increase (18 to 19 per cent) in 

 the rats underfed from three weeks of age, while Stewart ('19) 

 found a slightly larger increase in the underfed newborn rats. 



In adult rats during thirst the hypophysis changes but little in 

 absolute weight (Kudo, '21). 



DISCUSSION 



The changes in the average weights of the various organs and 

 parts in rats held at constant body weight for the various periods 

 are summarized in table 2. While no great emphasis can be laid 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 33, NO. 2 



