Page:The story of milk.djvu/50

 in milk at ordinary room temperature, 68° to 70°, which emphasizes the importance of keeping milk cool.

Relative growth of bacteria when held at different temperatures

+-+-+-++-         |   No. of  |           |           |          | Tem. of | bacteria  |  At end   |   At end  | At end of| At end of   Milk   |per c.c. at| of 6 hrs. | of 12 hrs.|  24 hrs. |  40 hrs.          | beginning |           |           |          | +-+-+-++-   °F. |          |           |           |          |    50    |    10     |    12     |      15   |       41 |        62    68    |    10     |    17     |     242   |   61,280 | 3,574,990 +-+-+-++-

Milk cooler

The diagram (after Conn) shows the rapidity with which bacteria multiply in milk not properly cooled. A single bacterium (a) in 24 hours multiplied to 5 (b) in milk kept at 50° F.; (c) represents the number that develop from a single bacterium in milk kept 24 hours at 70° F.

If the milk had contained 1,000 bacteria per cubic centimeter at the beginning, the part held at 50° F. would have contained 4,100 bacteria at the end of 24 hours, while that held at 68° F. would have contained