450 TOKUYASU KUDO 



In the adult rats the eyeballs lose nearly 10 per cent during 

 thirst (Kudo, '21). In young rats underfed (with water) from 

 three to ten weeks of age, Jackson ('15 a) found an increase of 

 nearly 50 per cent in the weight of the eyeballs. A still greater 

 increase (146 per cent) was found by Stewart ('19) in similar 

 experiments on newborn rats. 



Jackson ('15 a) thought the striking growth capacity of the 

 eyeballs during inanition might depend upon their large water 

 absorption, as the eyeballs are known to have a very high water 

 content. The present thirst experiments, however, indicate that 

 the remarkably persistent growth of the eyeballs continues even 

 when the water supply to the organism is greatly restricted. 



Notwithstanding the great increase in the size of the eyeballs 

 in the test rats, they do not protrude abnormally. More space 

 is doubtless provided for them, partly by actual growth of the 

 skeletal orbit and partly by atrophy of the orbital fat. 



HEART AND AORTA 



The heart (table 2) in the test rats shows an apparent slight 

 decrease in weight in the earlier periods with a small increase in 

 the later periods of thirst. It will be noted, however, that these 

 changes do not greatly exceed the differences between test rats 

 and controls in body weight, which are in the same direction. 

 The apparent changes in heart weight are therefore of doubtful 

 significance. 



In rats underfed from three weeks of age, Jackson ('15 a) like- 

 wise found no significant change of weight, although in underfed 

 newborn rats Stewart ('19) noted an increase of 26 per cent. 



During thirst in adult rats the heart likewise maintains its rela- 

 tive weight, losing in absolute weight nearly in proportion to the 

 entire body (Kudo, '21). 



Aorta. The aorta was cut proximally at the heart and distally 

 at the origin of the iliac branches. All branches of the aorta w^ere 

 clipped close to the vessel. All blood content w^as removed. The 

 following observations are too few (especially on controls) to war- 

 rant conclusions, but would seem to indicate an increase in the 

 weight of the aorta during the thirst experiments. 



