846 XIV. NUTRITIONAL VALUE OF FATS 



at an earlier period may be considered as having a higher nutritional value 

 than do regimens following which maturation is delayed. In tests made 

 by Deuel ei al.^~ it was found that the female rats receiving a fat-free diet 

 ad libitum matured at 81 days of age, whereas those receiving diets con- 

 taining different levels of fat experienced sexual maturity, on an average, 

 at periods as early as 65.1 days. The average occurrence of maturity for 

 the animals on the several levels of fat were as follows: 0% fat, 81 days; 

 5% fat, 70 days; 10% fat, 66.5 days; 20% fat, 65.8 days; 40%o fat, 65.1 

 days. In rats which had been fed on diets so low in calories, after weaning, 

 as to prevent an appreciable growth, sexual maturity did not occur.'* 

 However, as soon as the animals were allowed to consume various diets 

 ad libitum after the prolonged restriction period, sexual maturity took 

 place within a short time. The number of days required before sexual 

 maturity was noted, after the initiation of feeding the diets on an ad 

 libitum basis, were as follows: 0% fat, 14.7 days; 5% fat, 11.9 days; 

 10% fat, 10.5 days; 20%o fat, 7.7 days; 40%o, 9.8 days.'* It would thus 

 appear that, in the first instance, the sexual maturity occurred about as 

 well on the diets containing 10, 20 ,or 40% of fat, whereas in the animals 

 on the previously restricted diet the shortest time requirements for ma- 

 turity' were observed when the diets contained 20% of fat. It is uncertain 

 in the latter case whether the augmented effect, on the high-fat diets, in 

 promoting sexual maturity is a direct action exerted upon this function, 

 or whether it is an indirect result of the increased rate of growth. In 

 either case one would appear to be justified in interpreting the data as 

 indicative of the beneficial effect of fat in this change. 



(5) The Effect of Dietary Fat upon Pregnancy and Lactation 



Growth, pregnancy, and lactation entail successively increasing nu- 

 tritional stresses upon the animal which must be counteracted by means of 

 diets having progressively greater nutritional values. A dietary regimen 

 which may be satisfactory for providing optimal growth may prove un- 

 satisfactory for allowing a normal pregnancy, particularly if it is continued 

 over more than one pregnancy. Moreover, a regimen which proves en- 

 tirely satisfactory both for growth and for sustaining pregnancy may be 

 found to be inadequate in supplying the necessary dietary components to 

 insure a successful lactation. On this diet the mother may be unable to 

 nurse her litter successfully or to ensure the survival of healthy pups until 

 weaning. A number of authors have recorded the fact that reproductive 

 failure and unsuccessful lactation occur in rats raised to maturity on fat- 



