Young rhesus monkeys (Macaca mulatta) were given a diet containing casein, polished rice, whole wheat, salt mixture, sodium chloride, cod liver oil, and ascorbic acid. They developed a syndrome characterized by anemia, leukopenia, and loss of weight. Ulceration of the gums and diarrhea were common, and death occurred between the 26th and 100th day. 4 monkeys were given the deficient diet supplemented with 1 mg. of riboflavin daily, and these developed the characteristic signs and died. in periods of time similar to the survival of monkeys receiving the deficient diet alone. Nicotinic acid, either alone or in combination with riboflavin and thiamin chloride, failed to alter appreciably the course of the deficiency manifestations. Thus, it is evident that this nutritional cytopenia is not the result of a deficiency of vitamin B, riboflavin, or nicotinic acid.
The deficient diet supplemented with either 10 gm. of dried brewers' yeast or 2 gm. of liver extract (Cohn fraction G) daily supported good growth, permitted normal body development, and maintained a normal blood picture over long periods. It is obvious that yeast and liver extract contain a substance essential to the nutrition of the monkey which is not identical with any of those factors of the vitamin B complex that have been chemically identified. We have proposed the term vitamin M for this factor which prevents nutritional cytopenia in the monkey.