Journal of bacteriology . tion. The tenlargest colonies on each plate were measured. These data aregiven in table 3. These differences in size of colonies are presented graphicallyin figures 1,2, and 3. DISCUSSION It should be understood that the data here presented are in-tended to apply only to the routine examination of milk for whicha short period of incubation is used. Although the few data athand indicate that quite similar results are obtained with lowertemperatures and longer periods of incubation, it is not withinthe province of this paper to draw such conclusions. TABLE 3Size of colo
Journal of bacteriology . tion. The tenlargest colonies on each plate were measured. These data aregiven in table 3. These differences in size of colonies are presented graphicallyin figures 1,2, and 3. DISCUSSION It should be understood that the data here presented are in-tended to apply only to the routine examination of milk for whicha short period of incubation is used. Although the few data athand indicate that quite similar results are obtained with lowertemperatures and longer periods of incubation, it is not withinthe province of this paper to draw such conclusions. TABLE 3Size of colonies on plain and lactose agars DIAMETER OF COLONIES IN MICRONS NUMBER OF COLONY B. lactis-acidi(Culture A) B. lactis-acidi(Culture B) Streptococcus Plain Lactose Plain Lactose Plain Lactose 1 2345678910 50806050 607080606070 660720540520500640820540620580 340280320260240220300300300280 560 600 700 1300 600 640 590 1140 1080 1120 220 230220220240210240220260220 460440500480510580600570580640 Average 64 614 284 833 228 536. 15 ACia 1 (culture R) Fig. 1. The relative size of colonies of B. lactis-acidi grown on plain and lac-tose agars. Plates were incubated at 37°C. for forty-eight hours. Graphs areplotted from the average of ten colonies from each medium. 485 486 JAMES M. SHEKMAN Lactose agar was used in all of the tests herein reported, butfrom the results of a number of comparisons it may be said thatglucose is apparently just as efficient as is lactose, both as tonumber and size of colonies. According to the work of Heine-mann and Glenn glucose and lactose agars are of equal value
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