FOODS — HUMAN NUTRITION. 165 



and gained in weight. The conclusion is drawn that a small addition of yeast 

 (25 to 30 gm.) to the ordinary mixed diet is a desirable means of increasing its 

 nutritive value. 



The utilization by the animal organism of yeast cultivated in solutions of 

 sugar and inorganic salts, W. Volk (Ztschr. Spiritimndus., 38 {1915), No. 26, 

 pp. 235, 2S6). — Analytical data are given showing the composition of yeast 

 grown in a solution of sugar and inorganic salts. Feeding experiments with a 

 dog are also described, the results of which indicated that the coefficients of 

 digestibility for protein, fat, and carbohydrate were 85, 34.1, and 54.5 per cent, 

 respectively. The author concludes from these data that artificially cultivated 

 and brewery yeasts are equally valuable food materials and may be used oc- 

 casionally to replace meat in the diet. 



The digestibility of yeast, A. Loewy and von deb Heide {Berlin Kim. 

 Wchnschr., 52 {1915), No. 23, pp. 600, 601). — Metabolism experiments of seven 

 days' duration are reported in which each of the subjects (men) received 100 gm. 

 of yeast per day as a part of a simple mixed diet. Of the 79.35 gm. of protein in 

 the diet 31.69 gm. were furnished by the yeast and the remainder by the meat, 

 cakes, and potatoes, which formed the other ingredients of the ration. The 

 digestibility of the yeast protein for the first four days of the experiment was 

 estimated to be 81 per cent, and for the last three days, 85 per cent. 



A bacteriological study of retail ice cream, S. H. Ayers and W. T. John- 

 son, Jr. {U. S. Dept. Agr. Bui. 303 {1915), pp. 24, figs. ^).— The investigation re- 

 ported in this bulletin forms the first part of a study of the bacteria of ice cream. 

 The following problems were investigated : The number of bacteria in commercial 

 ice cream during the summer and winter months ; the determination of the 

 groups of bacteria found in commercial ice cream ; and a study of the relative 

 value of several different methods for the determination of Bacillus coll in ice 

 cream. Samples of ice cream representing 24 different manufacturers were pur- 

 chased at retail stores throughout the city of Washington, and represented the 

 ice cream as it is received by the consumer. Samples were collected in both the 

 summer and winter months. 



Examination of 65 samples of vanilla ice cream showed that their average 

 acidity was 0.206 per cent, calculated as lactic acid. No relation was found to 

 exist between the acidity of the samples and their bacterial content. 



The 94 samples of ice cream collected during the summer months showed an 

 average bacterial content of 37,859,907 per cubic centimeter, and the 91 samples 

 examined during the winter months showed an average bacterial content of 

 10,388,222. None of the summer samples contained less than 100,000 bacteria, 

 but the bacterial content of 14.28 per cent of the winter samples fell below this 

 figure. 



Employing the " milk-tube method," the bacteria in 71 summer samples and in 

 28 winter samples were divided into general groups of acid-coagulating, acid- 

 forming, inert, alkali-forming, and peptonizing organisms. The results of the 

 bacteriological examination are presented in detail and discussed extensively. 

 The authors state that " the bacterial groups bore much the same relation to 

 each other in the average summer and winter samples. There was, however, in 

 the summer samples a higher percentage of the acid-coagulating gi'oiip of bac- 

 teria and a lower percentage of the alkali and peptonizing groups than in the 

 winter samples." It was found that there was a higher percentage of rapid 

 acid-coagulating bacteria in ice cream during the summer months. In the sum- 

 mer samples, 52.81 per cent of the bacteria of the acid-coagulating group, and 

 in the winter samples 26.69 per cent, were active enough to coagulate milk in 48 

 hours when incubated at 30° C. The average number of peptonizing bacteria 



