diets. The total fat content of the diet was, of 

 course, a determining factor in the total content 

 of the individual fatty acids and was responsible 

 for the large amounts of oleic and linoleic acid 

 in the diets composed entirely of whole egg or egg 

 yolk. Although the linoleic acid content of the 

 egg-yolk diet was higher than that of the SPPB 

 diet, the total consumption of this fatty acid 

 when egg yolk was fed was about 60 percent of 

 the consumption for SPPB diet. The latter diet 

 supplied about eight times as much linoleic acid 

 as did the diet containing a comparable level of 

 fat, chiefly as butter fat. Linoleic acid, the only 

 fatty acid so far shown to be essential for the rat, 

 was present in all of the diets in amounts sufficient 

 to supply the 25 mg. per day reported {122) 

 necessary to prevent the development of skin 

 lesions in the young rat and to permit growth to 

 proceed at a normal rate. Linoleic acid as well 

 as other fatty acids may play a role in other 

 phases of lipid metabolism, but the importance 

 of specific fatty acid patterns in the nutrition of 

 the rat has not yet been established. 



The cholesterol content of the diets was rela- 

 tively low, amounting to less than 50 mg. per 100 

 grams of diet except for those diets containing egg. 

 The concentration of cholesterol was 478 mg. per 

 100 grams of SPE diet and was exceedingly high — 

 2,780 mg. per 100 grams — in the diet consisting of 

 100 percent egg yolk. 



Vitamins 



The data in table 5 summarizing the vitamin 

 content of the diets and the requirements for the 

 growing rat indicate that all of the vitamins 

 known to be required by the rat were supplied 

 in ample amounts. The high level of some of the 

 B vitamins in the semipurined diet and its modi- 

 fications was provided by the brewer's yeast, 

 which was present in all of these diets. Although 

 the thiamine content of the stock diet and of the 

 100 percent whole-egg or egg-yolk diet was low in 

 comparison with the other diets, it was sufficient 

 to supply the amount of this vitamin considered 

 essential. 



Choline requirements depend on many factors 

 (35) such as sex, strain, age, and dietary methi- 

 onine, cystine, betaine, or cholesterol. Although 

 10 to 20 mg. daily have been fed by many investi- 

 gators to supply the needs of the actively growing 

 rat, this amount is considerably more than is 

 necessary under some circumstances. In diets 

 containing from 24 to 30 percent casein, chloine 

 requirements are small (0 to 6 mg. daily). The 

 requirement of the rat over 30 days of age is also 

 small. According to Slanetz (173) only from 1 

 to 3 mg. daily are required by older rats. Although 

 the level of choline was low in most of the experi- 

 mental diets reported in this publication, the 

 amount supplied should be adequate for the adult 

 rat and even for the growing rat in view of the 

 methionine content of these diets. Levels con- 

 siderably in excess of requirements were provided 



by the diets containing egg or egg yolk unless the 

 high cholesterol content of these diets increased 

 the need for choline. 



Vitamins A, D, and E were not incorporated 

 into the diets, and the values recorded for these 

 vitamins are in terms of daily intake. The chief 

 source of vitamins A and D for all except rats fed 

 the stock diet was the supplement of percomorph 

 oil. Carotene from the kale supplement also con- 

 tributed to the vitamin A potency of the diets. 

 Egg and egg yolk were the only other foods to 

 provide significant amounts of this vitamin. The 

 supplement of <iZ-alpha-tocopherol acetate supplied 

 generous amounts of vitamin E compared to 

 reported requirements. 



Nerurkar and Sahasrabudhe (137) reported that 

 pure vitamin A is toxic to young male rats when 

 given orally at a dose of 40,000 I.U. daily. When 

 feeding was continued for 10 days, there was a 

 gradual decrease in the percentage retention of 

 calcium, phosphorus, and nitrogen. The toxic 

 dose of vitamin D is generally high, but no exact 

 data can be given. In man and dogs (161, p. 430), 

 20,000 I.U. daily may produce toxic symptoms. 

 The amounts of vitamins A and D in the experi- 

 mental diets under consideration in this publication 

 were in excess of requirements, but they were 

 considerably below the amounts that have been 

 reported to be toxic for relatively short-term 

 studies. 



Minerals 



The salt mixture used for preparing the semi- 

 purified diet was the chief source of minerals and, 

 as seen in table 6, relatively small differences were 

 observed in the ash content of these diets. The 

 stock diet contained from two and a half to three 

 times the ash content of the experimental diets, 

 and large amounts of calcium and phosphorus in 

 satisfactory proportions. Diets consisting of 100 

 percent egg or egg yolk were low in calcium, with 

 a ratio of calcium to phosphorus below the 

 desirable range. Potassium intakes were consider- 

 ably in excess of requirements. Manganese 

 tended to be low. Aluminum values have not 

 been included. The were high and variable be- 

 cause of comtamination with aluminum from the 

 grinders used in preparing these diets. 



Calories 



The data for the calorie values of the experi- 

 mental diets are summarized in table 7. In the 

 majority of the diets, sucrose was the chief carbo- 

 hydrate. The cereal starches supplied most of 

 the carbohydrate in the stock diet. Fat supplied 

 less than 20 percent of the gross calories from the 

 stock diet and from the various modifications of 

 the semipurified diet containing approximately 9 

 percent of fat. The remaining diets, except for 

 E100 and Y100, supplied 30 to 35 percent of the 

 calories as fat. The calories from fat in diet 

 Y100 were 74 percent of the total gross calories 

 from this diet. 



