Considerable work has been done by Freedman41 and others in ascertaining the identity of the substance stimulating the growth of yeast cells and its relation to the growth of bacteria. Working with a strain of hemolytic streptococci and pure yeast cultures, Freed-man was able to demonstrate that beef and beef heart infusions, peptone and autolysed yeast contained substances that are equally active with respect to the growth of these organisms. Certain specially prepared proteins such as casein, albumin, zein, fibrin, gelatin, edestin and orycinin apparently contain these substances which are active for bacteria. Freedman believes these active substances to be similar to, or identical with the yeast growth-promoting vitamin D.42

Pacini and Russell43 apparently demonstrated the presence of a growth-promoting substance in extracts of cultures of Bacillus typhosus. Thjotta also showed that a favorable influence is exerted on Bacillus influenzae by the addition of sterile bacterial extracts to the broth in which the organism is planted.44 On the other hand. Cooper 45 has found that extracts of Bacillus coli have no effect in relieving polyneuritis in pigeons. Damon 46 has endeavored to throw further light on the subject by feeding to rats the products of the growth of Bacillus paratyphosus B, Bacillus coli and Bacillus subtilis. The administration of the bacteria was carried out in the following way: The organisms were grown in flasks containing 100 cc. of the medium, then killed by autoclaving at 120° for fifteen minutes - a procedure that would not affect the vitamin content as has been demonstrated by McCollum, Simmonds, and Pits.47 The culture was then concentrated by evaporation on the steam bath to about 15 to 20 cc. and finally the organisms were taken up on starch by desiccation in a shallow pan at a reduced pressure. This starch bearing the bacteria was then used to replace an equivalent amount in the basal ration and the effect of bacteria noted by observing the trend of the weight curve.

No indication was found that water-soluble B was formed by the organisms examined.

41 Am. Food Jour. Oct. 1921.

42 In yeast there is present some constituent, soluble in 70 to 95 per cent alcohol and still more soluble in water, which, when added in small amounts to a medium in which yeast is grown, will increase the invertase activity of yeast to a remarkable extent (Miller, J. Biol. Chem. 48, 329, 1921). This substance, however, is not identical with the growth stimulant.

43 J. Biol. Chem. 34, 43, 1918.

44 J. Exp. Med. 33, 763, 1921.

45 J. Hyg. 14, 20,1914.

46 J. Biol. Chem. 48, 379, 1921.

47 J. Biol. Chem. 99, 521, 1917.

Suguira and Benedict48 have suggested the possibility that milk contains still another accessory substance which is lacking in yeast. They base this hypothesis on their observation that a diet of bananas, casein, and yeast is entirely satisfactory for growth and reproduction of rats but is not sufficient to permit of rearing the young, while the addition of 10 cc. of cows' milk to the diet of the mother resulted in normal growth of the sucklings. The necessary addition could be obtained from "protein-free milk " 49 but not from purified lactose or the inorganic constituents of milk.

48 Suguira and Benedict, J. Biol. Ghem. 40, 449, 1919. 49 See pp. 9,10.