EFFECTS OF THIEST ALBINO RATS 459 



Comparing my results in young rats on thirst tests with those 

 of Jackson ('15 a) in young rats of similar age held at constant 

 body weight by underfeeding (with water allowed) , there is found 

 a remarkable similarity between them. Thus, in both cases 

 there is a marked growth in the brain, spinal cord, eyeballs, hy- 

 pophysis, skeleton, suprarenals, and alimentary canal. In both 

 series the brain, musculature, and heart remained nearly con- 

 stant, and the thymus, ovaries, spleen, thyroid, and integument 

 decreased greatly in weight. There are some differences between 

 the results of the thirst and the inanition tests, however. The 

 kidneys appear to gain markedly during thirst, but remain con- 

 stant during inanition. The testes lose heavily in weight during 

 thirst, but gain markedly during inanition. Other forms of 

 partial inanition give results differing more or less from the fore- 

 going, as shown by the experiments of Hatai, Osborne and Mendel, 

 McCarrison, and others on diets defective in various respects, 

 including vitamine deficiencies (cf. Jackson and Stewart, '19, 

 and Kudo, '21). 



It has also been shown by Jackson and Stewart that the 

 changes in organ weight during inanition differ greatly according 

 to the age of the animals. Thus, the changes during underfeeding 

 in the newborn are very different from those in adolescent rats 

 and these in turn differ from those in older animals. The age 

 factor is doubtless equally important in the effects of thirst upon 

 the weight of the various organs. 



SUMMARY 



The principal results of the present investigation may be 

 briefly summarized as follows. 



Albino rats about one month old may be held at constant body 

 weight for several weeks by a restricted amount of liquid (milk) 

 in a diet otherwise adequate for growth. The rats show a pro- 

 gressive tolerance of thirst, so that less liquid milk is daily re- 

 quired for maintenance as the experiment proceeds. 



The tail becomes elongated while the body length remains 

 constant. 



