136 PRACTICAL DAIRY BACTERIOLOGY 



morning's milk soon contains many more bacteria than the milk 

 that is twelve hours older, and hence it sours much more 

 quickly. The lesson to be drawn from this is the necessity of 

 immediately cooling the milk to a temperature as low as 40, 

 if possible. It should be remembered, too, that it is just as 

 necessary to cool good milk as it is to cool dirty milk. Unless 

 this is done the good milk will soon contain as many bacteria 

 as the dirtiest milk. 



It should be recognized, however, that the value of the cooling 

 of the milk is only to decrease the rapidity of the multiplication 

 of the bacteria and does not necessarily affect its healthfulness. 

 The milk, as we have seen, may distribute the germs of certain 

 diseases. If these germs have found their way into the milk, 

 the fact that the milk has been cooled will not destroy them and 

 will have no value in rendering the milk wholesome. None of 

 the disease germs known to be found in milk would be killed, 

 or even injured, by the temperature of the ice chest, at least 

 if continued only for a few hours, and therefore the practice 

 of cooling the milk cannot be looked upon as a safeguard for 

 protecting the public from the specific diseases liable to be dis- 

 tributed by it. On the other hand, the development of the 

 diarrheal diseases which, as we have learned, probably come 

 from poisons secreted in the milk by certain kinds of bacteria 

 may, perhaps, be checked by the use of cool temperatures that 

 will prevent the growth of bacteria. Concerning this we know 

 practically nothing at the present time. The value of the im- 

 mediate cooling of the milk, therefore, is primarily in making 

 the milk keep longer, and not in rendering it more wholesome. 

 It decreases numbers only and does not remove disease germs. 

 Any method that cools the milk rapidly is satisfactory. It may 

 be done by immersing it, already bottled, into cold water. This 

 has the advantage of cooling it rapidly in the jar so that no 

 further disturbance of the milk is necessary. Cooling in cans 

 is less desirable since the milk must afterward be handled again. 



