duplicate analysis. Once the conditions had been 

 established for producing a uniform homogenate 

 from the kidney, the results from chemical analyses 

 showed excellent reproducibility. It then seemed 

 preferable to analyze individual kidneys to permit 

 a direct comparison of the results with the other 

 measurements under consideration and to avoid 

 masking differences that may result from average 

 values. Only one analytical value could be 

 obtained for kidneys weighing 2 grams or less. 

 Duplicate values were obtained when sufficient 

 material was available. 



The methods for analysis of tissues were the 

 same as those used for the food samples, except 

 that fat determinations were done by the AOAC 

 acid hydrolysis method (13). The coagulable 



protein in the freshly collected urine samples was 

 determined by precipitating with 5 percent acetic 

 acid (68) and weighing the washed, dried precipi- 

 tate. Blood serum samples collected at the time 

 of sacrifice were stored, refrigerated, at 4° C. until 

 analyzed for cholesterol and for the various protein 

 components. Serum cholesterol was determined 

 by the direct method of Zlatkis, Zak, and Boyle 

 (192). It has been established (108) that the 

 values obtained by the use of the direct method 

 are high, but further investigations in this labora- 

 tory have indicated that the relationships reported 

 here are substantially correct. Serum protein 

 components were determined by electrophoretic 

 analysis, using the method of Tiselius (183) as 

 modified by Longsworth and Jacobsen (118). 



Results and Discussion 



Composition of Experimental Diets 



On the basis of current information, the majority 

 of the diets investigated provided adequate 

 amounts of the nutrients essential for the growing 

 rat and amounts generaUy considered adequate or 

 more than adequate for maintenance of the adult 

 animal. Admittedly, our knowledge of the re- 

 quirements of the rat at various stages of life is 

 far from complete. 



The analyzed or calculated values for the 

 nutrient content of the diets are summarized in 

 tables 2 through 7. Corresponding information 

 for the ingredients used in preparing these diets 

 is summarized in tables 75 through 78 of the 

 appendix. To facilitate evaluation of the 

 adequacy of the experimental diets under con- 

 sideration, the amounts of nutrients suggested 

 as requirements for the growing rat and for the 

 adult rat have been included when such informa- 

 tion was available. Many factors may influence the 

 requirement for a specific nutrient such as the 

 heredity of rats under investigation and the pro- 

 portion of other dietary components. Most of 

 the values for nutrient requirement that are re- 

 corded represent the average of results obtained 

 by several investigators, and have been limited to 

 requirements of rats fed relatively simple diets 

 similar to the semipurified diet used in the in- 

 vestigations reported in this bulletin. 



Protein 



The protein content (table 2) of all but three of 

 the experimental diets was within the range of 25 

 to 30 percent of the diet — an amount suggested 

 for optimum growth of the rat. Two diets, SPM 

 with 23.8 percent protein and SPW with 24.6 

 percent protein, were only slightly below the 25- 

 percent level; the third diet, consisting of 100 

 percent whole egg, provided a considerable excess. 

 The stock diet contained most of the essential 

 amino acids in relatively small amounts when 

 compared with the other diets under investigation 

 but still provided sufficient amounts to meet 



requirements. The diet consisting of 100 percent 

 egg with its high protein content supplied the 

 essential amino acids in amounts considerably in 

 excess of requirements. The other diets provided 

 from two to four times the amount of the essential 

 amino acids required for the growing rat, and still 

 greater excesses for the adult animal. Considering 

 tryptophan as the base line, no marked differences 

 in the amino acid patterns of these diets were 

 observed except for stock and SPW diets. The 

 stock diet contained relatively small amounts of 

 tryptophan when compared with the other amino 

 acids. Methionine and cystine were high in 

 SPW diet in relation to its tryptophan content. 



Fat 



Data for the fatty acid composition of the diets 

 are presented in table 3 as a percentage of the 

 dietary fat and in table 4 as a percentage of the 

 diet. No data were available for the fatty acid 

 composition of yeast fat, and the results recorded 

 are exclusive of the fat from this source. The 

 small amount of fat in the yeast (0.5 percent or 

 less of the diet) would not be sufficient to change 

 materially the major characteristics of the dietary 

 fat. Table 3 also includes the iodine values for 

 the dietary fats, and table 4 includes the choles- 

 terol content of the diets. 



The iodine values of the food fats (table 3) 

 ranged from 33.4 for SP 8 butter or SP 16 butter 

 to 87.8 for SPPB diet, reflecting the relatively 

 high linoleic acid content of peanut butter. Of 

 the fat in SP 8 HVO, SP 16 HVO, SPa 16 HVO, 

 SPb 8 HVO, SPEW, and SPW diets, more than 

 60 percent was oleic acid. Saturated fatty acids 

 of chain length 16 or less accounted for more 

 than 40 percent of the fat in the diets containing 

 8 and 16 percent butter. 



The concentration of fat in these diets (table 4) 

 differed widely, with the smallest amount 6.3 

 percent in the stock diet and the largest amount 

 58 percent in the diet consisting of 100 percent 

 egg yolk. Although the daily intake of the 

 latter diet was less, fat consumption was higher 

 on this diet than on any of the other experimental 



