involved in the utilization of these diets. Cystic 

 damage appeared to be somewhat reduced when 

 vitamin B 6 was added to the diet, with or without 

 chohne. Calcium ratings were particularly high 

 for rats fed the diets containing supplements of 

 ascorbic acid with or without added cholesterol. 



When the level or kind of fat, or both, were varied, 

 the extent of the kidney damage observed was 

 more like that found with the semipurified diet 

 than with SPE diet. Damaged kidneys were 

 seen frequently but no marked differences were 

 observed in these moribund rats that could be 

 ascribed to the kind or level of fat. Extensive 

 degenerative changes, apparent from gross ex- 

 amination of five kidneys that were not suitable 

 for microscopic examination, indicate that the 

 lower rating for the kidneys from rats fed SP 16 

 HVO was without significance. When the level 

 of protein was increased, the results were similar 

 to the results with SP 8 HVO diet when differences 

 in weight loss before sacrifice were considered. 



Microscopically, the kidneys and livers of rats 

 fed the diet containing 30 percent egg yolk (SPEY) 

 appeared similar to those from comparable rats 

 fed SPE diet. The damage observed in the 

 kidneys from rats fed the diet containing egg 

 white (SPEW) was less extensive than that ob- 

 served with SPE diet and resembled that seen in 

 moribund rats fed the semipurified diet. Less 

 extensive kidney damage occurred when the diet 

 contained 100 percent whole egg than when the 

 diet contained 25 percent egg (SPE), paralleling 

 the longer survival of rats fed El 00 diet. 



The microscopic appearance of the kidneys 

 from rats fed 100 percent egg yolk differed sig- 

 nificantly from that observed with the other diets 

 containing whole egg or egg fractions. Cystic or 

 glomerular damage was small; calcium deposits 

 were heavy, even in rats showing relatively small 

 weight loss, and were not necessarily associated 

 with extensive cystic damage or fibrosis. Most 

 of the rats fed 100 percent egg yolk were sacrificed 

 before weight loss exceeded 100 grams, but there 

 was no evidence of a marked increase in cystic 

 or glomerular damage with increasing weight loss. 

 The results from microscopic examination of 

 tissues from rats fed diets consisting solely of 

 whole egg or containing high levels of egg yolk 

 or egg white contrast with those for rats fed 25 

 percent egg (SPE), and provide further evidence 

 that ingredients in the SPE diet other than egg 

 must be contributing to the acceleration of the 

 degenerative changes that occur on this diet. 



Further evidence of this was obtained from a 

 group of 15 rats, 5 fed SPE diet, 5 fed 100 percent 

 egg yolk, and 5 fed 97 percent egg yolk supple- 

 mented with 3 percent salt mixture. The rats 

 were scheduled for sacrifice at 450 days of age. 

 When a rat on any one of the three diets became 

 moribund and was sacrificed before 450 days, the 

 corresponding littermates fed the other diets were 

 sacrificed at the same time. Two of the rats fed 

 SPE diet became moribund at 396 and 398 days 



of age, and 1 rat fed 100 percent egg yolk was 

 losing weight before reaching 450 days of age. 

 The 5 rats fed egg yolk supplemented with the 

 salt mixture appeared healthy at the tune they 

 were sacrificed. The histological findings for the 

 kidneys from these rats suggest that the shortened 

 lifespan of rats fed a diet containing 100 percent 

 egg yolk was due, in part at least, to a mineral 

 imbalance and was not accompanied by marked 

 degenerative changes such as were seen in the 

 kidneys of rats fed SPE diet. The kidneys of rats 

 fed the egg yolk diet supplemented with 3 percent 

 of a salt mixture containing the mineral elements 

 considered essential were generally normal in 

 appearance and showed no evidence of calcium 

 deposition. 



In table 18 are also included the results of 

 microscopic examination of tissues from rats that 

 were changed after 250 days from stock to SPE 

 diet or the reverse. The kidneys from rats that 

 were maintained throughout life on stock or SPE 

 diet were typical of those already discussed for 

 these diets, with the high glomerular damage in 

 the kidneys from rats fed the stock diet and high 

 cystic damage and heavy calcium deposits in those 

 from rats fed SPE diet. When the diet was 

 reversed, kidney damage was less extensive with 

 both diets, and these animals lived longer than 

 did the other littermates that were continued on 

 either stock or SPE diet. 



Influence of heredity. — Wistar rats were 

 much less susceptible to kidney damage than were 

 the BHE strain. Of the nine kidneys examined 

 from rats fed SP 8 HVO diet, only one from a rat 

 848 days old was badly damaged; on SPE diet, 

 two of the nine kidneys showed marked degenera- 

 tive changes, one from a rat 397 days old and one 

 from a rat 846 days old. No calcium deposits 

 were seen on either of these diets, and the marked 

 difference in the response of BHE rats to SP 8 

 HVO and SPE diets was not apparent with Wistar 

 rats. The differences in the response of these two 

 strains of rats did not appear to be due to the 

 dietary history of the parent rats. A similar 

 difference in the response of BHE rats to SP 8 

 HVO or SPE diets was observed whether the 

 parents were raised on the usual stock diet or on 

 the diet that was used to raise the Wistar stock 

 rats. 



Discussion. — A tendency for chronic nephritis 

 to occur in the older rat has been observed by 

 many investigators. The extent of the kidney 

 damage found was generally less than that re- 

 ported in this publication for BHE rats. Results 

 reported elsewhere have dealt chiefly with the 

 occurrence of nephritis in older rats without re- 

 gard to diet. Saxton and Kimball (168) found 

 chronic nephrosis in 44 percent of the kidneys from 

 rats dying naturally, and considered that this condi- 

 tion occurred spontaneously in the albino rat. De- 

 generative changes in the kidneys were rarely seen 

 in young rats, and the incidence of kidney damage 

 increased with age up to 800 days. There was a 



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