. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 14 BULLETIN 303;, U. S. DEPARTMENT OF AGRICULTURE. Among this group there are a large number of different types of organisms. Many rapidly peptonize the casein of milk and render milk alkaline or slightly acid, while others first attack the lactose and only produce a slight peptonization after several days' growth. From the milk-tube method of differentiation of the bacterial groups it was possible to gain some information as to the extent of these different classes of peptonizers. In Table 9 are shown the average perc
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 14 BULLETIN 303;, U. S. DEPARTMENT OF AGRICULTURE. Among this group there are a large number of different types of organisms. Many rapidly peptonize the casein of milk and render milk alkaline or slightly acid, while others first attack the lactose and only produce a slight peptonization after several days' growth. From the milk-tube method of differentiation of the bacterial groups it was possible to gain some information as to the extent of these different classes of peptonizers. In Table 9 are shown the average percentages of the peptonizing group in summer and winter samples of ice cream. Based on the 14-day reaction among the summer so. % % % $ 8 18 ° •*) & *0 VO N B § % % 13 ? § § !o P !o R 15 /='£:f?C£'U7XGE OF 70TAL BACTER/A Fig. 4.—Frequency curve showing percentage of peptonizing bacteria per cubic centimeter of ice cream, summer and winter series combined. samples, per cent of the bacteria belonged to the peptonizing group. According to the 2-day reaction, there were per cent. Therefore per cent of the peptonizing bacteria were sufficiently active to produce a peptonization within two days. Among the winter samples per cent of the peptonizing bacteria were suffi- ciently active to peptonize milk within 48 hours. These active peptonizing bacteria are more important than the slower-acting varieties, since their peptonizing action is usually more complete than that of the latter-named varieties, and if any harm is produced by this group, they are most likely to be the organisms concerned. Table 9.—Changes in the percentage of the peptonizing group of bacteria in ice cream when determined by litmus-milk reactions after various lengths of incubation. Peptonizing group. Per cent reacting after incu- bation for— 2 days. 5 days. 14 days. Average of 71 summer samples. Average of 28 winter Per cent. Per cent. Per cent.
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