and generally were accompanied by enlarged and 

 damaged kidneys. 



A rapidly moving protein component in the 

 blood serum of rats was observed occasionally 

 at all ages and on all diets. The percentage of 

 rats with this component in their sera, as well as 

 the amount present, varied with age and with diet. 

 The presence of small amounts of PA observed 

 occasionally in young rats seemed to bear little 

 relation to diet. When high levels of this compo- 

 nent were observed, they were usually associated 

 with extensively damaged kidneys and elevated 

 serum cholesterol levels. 



Histological and biochemical investigations of 

 the tissues of moribund rats measure only terminal 

 stages and provide little information concerning 

 the intermediate steps leading to death and the 

 effect of diet thereon. 



More extensive studies dealing with the 

 changes that occur at different stages of the life 

 cycle are needed to establish the role of diet in the 

 sequence of events that determine length of life. 



The limited data for Wistar rats fed the semi- 

 purified diet and the diet containing 25 percent 

 egg indicate that the response to diet may differ 

 markedly with the strain of rats under investiga- 

 tion. Wistar rats lived longer than BHE rats fed 

 both diets, with greater differences observed when 

 the egg-containing diet was fed. Even in older 

 rats of the Wistar strain, kidney damage was 

 rarely seen and appeared to be unrelated to the 

 diet. 



To explain such differences in the response to 

 diet, comparative data for different strains of 

 animals should include measurements to detect 

 basic differences in tissue enzymes and in the 

 metabolic pathways controlling the utilization of 

 various experimental diets. The possibility of 

 detecting inherent differences at an early age 

 and of controlling or preventing by dietary means 

 the adverse effects due to heredity also warrants 

 further consideration. 



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