184 AGRICULTURAL BACTERIOLOGY. 



original high temperature is retained they multiply rapidly and 

 the few thousands are soon likely to become hundreds of 

 thousands or millions. For example, milk tested at intervals 

 for twenty-four hours showed the following increase : 



When first received, 153,000 per cu. in. 



After I hour, 616,000 " " 



After 7 hours, 1,020,000 " " 



After 24 hours, 85,000,000 " " 



The rapidity of multiplication is dependent directly upon 

 temperature, being greatest at temperatures of 80 to 100 F. 

 At temperatures as low as 50 F., the rapidity of growth is 

 much decreased, and below 40 F. it is very slight. When the 

 temperature of freezing is reached the growth stops entirely. 

 At freezing temperature the milk may be preserved indefinitely 

 without bacterial growth. 



These facts explain the statement made that the matter of 

 temperature is of more importance in connection with the 

 keeping quality of milk than even the original cleanliness. No 

 matter how careful a dairyman may be in obtaining clean milk, 

 if he allows it to remain warm the few bacteria which did get 

 in will multiply so rapidly that they will soon be as numerous 

 as they are in another sample of milk which at first contained 

 larger numbers but had been cooled. Milk carelessly drawn 

 but properly cooled will keep better than milk carefully drawn 

 but not properly cooled. Nearly all of the phases of the gi- 

 gantic milk industry of civilized communities are based chiefly 

 upon the various devices for keeping the milk properly cool, 

 in order to prevent the growth of bacteria until it may be con- 

 veniently delivered to the consumer. The milk dealer has 

 discovered that the growth of bacteria ruins his milk and that 

 his only effectual remedy against them is the use of low tem- 

 peratures. The bacteriologist teaches him further that the 

 milk should be cooled immediately after the milking, for the 

 obvious reason that the milk is then at a temperature which 



