VETERINARY MEDICINE. 769 



experience, the group count agrees somewhat closely with the plate count- 

 agreeing, indeed, about as closely as the plate counts of different laboratories 

 agree with each other. Raw, fresh milk does not contain any appreciable 

 number of dead bacteria which might disclose themselves to the microscope, but 

 fail to grow in plates. 



The direct microscopical examination of milk smears by the Breed method 

 (E. S. R., 31, p. 372) will classify raw milk into grades A, B. and C with about 

 the same accuracy and much more quickly than will the plate method of 

 bacteriological analysis. It can not be used in the study of pasteurized milk, 

 however, since it discloses dead as well as living bacteria, except as indicating 

 when such milk has become old before it is pasteurized by showing large num- 

 bers of dead bacteria with small numbers by the plate method. The direct 

 method might be of exceptional value applied at the dairy to guide the dairy- 

 man as to the general grade of the milk he is marketing. It may also be of 

 great aid to the large dealer to enable him to determine promptly whether he is 

 purchasing milk of A, B, or C grade. The possibility of quick results and ea.se 

 of making the smears at the dairy or shipping station, .subsequently sending 

 them to the laboratory for microscopic examination, renders the method espe- 

 cially applicable at the dairy end of the line. 



Sm^oothness and keeping qualities in ice cream as afEected by solids, W. K. 

 Bbainerd (Virginia Sta. Tech. Bui. 7 (1915), pp. 154-159, figs. 9; Rpts. 1913-14, 

 pp. 154-159, figs. 9). — Fi-om a micro-photographic study of ice cream the 

 author concludes that smoothness and keeping quality or stability of texture of 

 ice cream are closely associated. Smoothness depends upon the amount and 

 fineness of division of solids present other than those in true solution, within 

 limits; that is, the smoothness depends upon the size and distribution of ice 

 crystals, which in turn depend upon the number and nearness together of minute 

 solid particles which interfere with crystallization and reduce the size of the 

 Ice crystal. 



Colloidal solutions of solids other than fat are deemed best adapted to ice- 

 cream making, and the finer their division and the more complete the emulsion 

 of the fats the better. The homogenizer has its application in this respect. 



The lieeping qualities of ice cream apparently depend upon the stability of the 

 " mix." The keeping qualities of ice cream made from a given mixture will 

 depend upon the disposition of the solids in that mixture to separate from the 

 liquid, which in turn depends upon the fineness of division of the solids. The 

 finer the division the better the keeping qualities up to the point at which the 

 solid merges into a true solution. 



VETERINARY MEDICINE. 



Studies in acid-fast bacteria, I-X, A. I. Kknu.\ll, A. A. Day, and A. W. 

 Wat.kkb (Jour. Infect. Diseases, 15 (1914), No. S, pp. 417-471). — The first of 

 these studies is on the metabolism of saprophytic human tubercle bacilli in 

 plain, dextrose, mannit, and glycerin broths. " Young, rapidly-growing tubercle 

 bacilli appear to be, in part at least, nonacid-fast. The strain of avirulent 

 tubercle bacilli studied here exhibit the Theobald Smith reaction characteristic 

 of the growth of human tubercle bacilli in glycerin broth. Neither dextrose, 

 mannit, nor glycerin appears to exert any marked sparing action for the protein 

 constituents of ordinary media. Ammonia accumulates rather rapidly during 

 the first, second, and third weeks of gi-owth of tubercle bacilli in plain, dex- 

 trose, mannit, and glycerin broths, followed by a definite well-marked recession, 

 during which this ammonia detectable in the media gradually diminishes in 

 amount. The cause of this recession is unknown." 



