McCay, Maynard, Sperling, and Osgood (121) 

 reported a correlation of kidney weight with level 

 of protein when diets containing 8, 14, and 20 

 percent casein were fed. These dietary regimens 

 were initiated during the latter half of life and 

 did not involve excessively high levels of protein. 

 The kidney size reflected dietary protein level at 

 death in spite of the wasting that accompanied 

 the last diseases of old age. Addis, Lippman, 

 Lew, and others (5) found that kidney size in- 

 creased when the level of egg, liver, wheat germ, 

 or casein was increased from 10 to 60 percent, and 

 that the extent of the enlargement depended upon 

 the source of protein. Smith and Moise (174) 

 reported that, after removal of one kidney, the 

 remaining kidney became enlarged and that the 

 increase was proportional to the level of dietary 

 casein. 



Agreement with regard to the cause of increased 

 kidney size as the result of feeding high levels of 

 protein has been less general. Addis, Lippman, 

 Lew, and others (5) suggested that the differential 

 effect of dietary protein upon kidney size was not 

 due to differences in its inherent nutritive value 

 for the kidney but was secondary to the work 

 load imposed upon the kidney by urea excretion. 

 Other investigators (138, 150) conclude that the 

 load on the kidney from increased urea excretion 

 is not responsible for kidney enlargement on the 

 basis of the results of feeding high levels of urea. 



In general, the data available on the size of 

 liver of rats are similar in nature to those reported 

 for the kidney, and have also indicated a close 

 relationship between liver and body weight. 

 Donaldson (50) has reported a value of 18.7 grams 

 (4.2 percent of body weight) for the liver from 

 fasted male rats weighing 450 grams. Liver 

 weights of 12.1 and 16.4 grams have been reported 

 by Freudenberger (70) for 1 -year-old male rats of 

 the Wistar and Long-Evans strain, respectively. 

 The Wistar rats weighed 340 grams; the Long- 

 Evans rats, 458 grams. No strain differences 

 were apparent, since the livers of both strains 

 represented the same percentage of body weight 

 (3.6 percent). Addis and Gray (4) reported still 

 smaller liver weights for the Slonaker strain, with 

 the values representing 3.0 to 3.2 percent of the 

 body weight in animals weighing between 360 and 

 410 grams. These last-named investigators sug- 

 gested that a possible explanation for the differ- 

 ences observed may lie in the higher protein level 

 of the diets fed the rats with the larger livers. 

 For rats 1 to 2 years of age, Yiengst, Barrows, 

 and Shock (191) observed liver weights for the 

 McCollum strain of rats of 13.3 and 13.0 grams, 

 representing 2.8 and 3.0 percent of the body 

 weight, respectively. No significant change with 

 age was observed. 



Several investigators reported results indicating 

 that liver weight may be influenced by diet without 

 comparable changes in body weight. Blather- 

 wick, Medlar, Bradshaw, and others (81) reported 

 variations in this percentage from 2.8 to 5.2. 



Addis, Lippman, Lew, and others (5) obtained an 

 increase in liver weight of approximately 10 

 percent, with no comparable increase in body 

 weight, when rats were fed 60 percent wheat 

 germ, liver, or egg powder for a period of 20 days. 

 At the 10-percent level, diets produced no change 

 in liver weight. Casein was without influence at 

 either the 10- or 60-percent level. McCay, 

 Maynard, Sperling, and Osgood (121) reported a 

 10-percent increase, not accompanied by a com- 

 parable increase in body weight, when the level 

 of casein in the diet was increased from 8 to 20 

 percent and the rats were fed the experimental 

 diets from middle age until death. Large livers 

 have been reported in rats fed diets containing 

 high levels of egg (156) or liver (31). 



Even with the stock diet, BHE rats were 

 relatively large animals, but in spite of their 

 large body weight the livers of the fasted rats 

 were generally smaller than those reported by 

 many investigators. The livers from fasted rats 

 on the stock diet were similar in size and in 

 percentage of body weight to those reported by 

 Yiengst, Barrows, and Shock (191). Liver weights 

 of 10 grams reported by Reussner and Thiessen 

 (156) for 9-month-old rats fed a diet of cereal, 

 milk, and sugar or milk alone were similar to 

 those obtained with BHE rats of comparable 

 size fed most of the experimental diets. The 

 average liver weight of 15 grams observed by 

 these investigators for rats fed a bacon and egg 

 diet containing 22 percent egg was similar to 

 that obtained for BHE rats fed SPE diet, when 

 considered as percent of body weight. 



Harrison (85) reported relatively small differ- 

 ences between the liver weight of young fasted 

 and nonfasted rats fed stock ration. A search of 

 the literature has failed to reveal investigations 

 showing differences in the liver weights of fasted 

 and nonfasted rats of the magnitude observed 

 with BHE rats fed the semipurified diet or its 

 modifications. 



Summary. — A kidney weighing less than 1.8 

 grams was generally normal in appearance. 

 Degenerative changes were usually apparent when 

 the kidney weight exceeded 1.8 grams, and cystic 

 and glomerular damage as well as hyalin casts 

 were usually observed when the weight exceeded 

 3 grams. 



In fasted rats that were maintaining their weight, 

 differences in kidney or liver size in relation to 

 age and to diet were frequently associated with 

 parallel differences in body weight. Large kidneys 

 and livers were observed in some of the older 

 rats fed all diets. Kidneys tended to be large 

 in rats 300 days and older fed SPE diet, regardless 

 of body weight. Large livers were found even in 

 young rats 200 to 300 days of age that were fed 

 this diet. Although there was a tendency for 

 kidney or liver weight to parallel body weight, a 

 somewhat closer relationship was observed between 

 kidney and liver weights, at least in rats fed stock 

 or the semipurified diet. 



51 



