Using albino rats weighing 210-280 and 300-400 grams, identical experiments were carried out twice to study the effect of dietary protein level on the nitrogen regeneration of the liver. The rats were divided into two groups and were fed ad libitum with 20% and 10% casein diets respectively. During the preliminary,period of three weeks, the average food consumption of rats in both groups were the same. Both diets were found to be adequate in maintaining the body weight of the animals.The experiment was continued for three consecutive periods: the normal period (7 days), the fasting period (2 days) and the regeneration period (4 days). During the normal and regeneration periods the rats were fed with their respective original diets. At the end of each period, the body weights of the animals were determined and one third of the animals in each group were killed for analysis of liver nitrogen. In the first experiment nitrogen balance in each period was also determined and in the second experiment some internal organs other than liver were weighed.It was found that the level of protein in the diet had no effect on the body weight or the weight of the internal organs, but had significant effect on nitrogen balance and the content of nitrogen in the liver. The liver nitrogen fell to the same level after two days fasting irrespective of the original content. Significant correlation was found between nitrogen balance and food intake of the rats in the 10% casein group, and between the liver nitrogen content and food intake in the 20% casein group. As the energy intakes of both groups in the two experiments were above 1200 Cal. per square meter of body surface, the effect of nitrogen retention could not be due to the caloric intake (Benditt et al) but to the net amount of protein ingested. The possibility of using a 10% level diet for estimating the biological value of protein with the method of nitrogen regeneration in liver is discussed.

Vegetarian and mixed diets, supplying about 3000 Cal. and 8,5 gms. of protein daily, were given alternately to 6 adult men of 22-34 years old. In the vegetarian diet, composed of cereals, legumes and vegetables, about 20% of the total protein were supplied by the legumes. In the mixed diet, the legumes and part of the cereals of the above were replaced by meats, eggs and milk, furnishing about 50% of the total protein. The experiment consisted of 5 consecutive periods of 10 days each in the first three periods and 5 days each in the last two.Urinary nitrogen excretion of the experimental subjects during the period on vegetarian diet was lower than that on mixed diet. When the diet was changed from vegetarian to the mixed ration, urinary nitrogen remained low in the first two days and increased from the third day. However, when the change of diet was reversed, there was an immediat'e decrease of nitrogen excretion. The nitrogen balance was in favour of the vegetarian diet.The essential amino acid contents of the vegetarian diet were lower than that of the mixed diet. Therefore, better utilization of the protein in the vegetarian diet cannot be satisfactorily explained by essential amino acid index. With adequate caloric intake, 85 gms. of protein supplied daily either by vegetarian or by mixed diet may maintain nitrogen balance and protein storage in adult man.