I 86 AGRICULTURAL BACTERIOLOGY. 



depends upon three factors, (i) The original cleanliness of 

 the farmer in his cow shed and dairy. (2) The age of the 

 milk. (3) The temperature at which the milk has been kept, 

 including the quickness of the original cooling. The farmer 

 can improve the keeping quality of the milk by improving the 

 conditions of his dairy and by better devices for cooling ; the 

 shipper can have no less influence upon it by controlling the 

 matter of temperature, and the consumer has no less a respon- 

 sibility in regulating the temperature at which he keeps the 

 milk and the quickness with which he uses it. 



The question is frequently asked, what number of bacteria 

 milk must contain before it is to be condemned. This ques- 

 tion cannot be answered. It may contain a very few but be 

 extremely dangerous, or it may contain millions and be harm- 

 less. It is sometimes stated that if it contains more than 50,- 

 ooo per c.c. it is not fit to drink. If this is accepted then most 

 of the milk of our larger cities is unfit to drink, for rarely does 

 such milk contain less than several hundred thousands. The 

 fact is that the numbers of bacteria can tell us little as to the 

 healthfulness of milk. On a later page it will be seen that 

 cream which is made into butter contains bacteria by hundreds 

 of millions or even billions per c.c., but no one regards this as 

 indicating that the cream or the butter is dangerous. Of course 

 we want our milk as free from bacteria as possible, but where 

 a line can be drawn between good and suspicious milk no one 

 can say. Provided the bacteria are of the lactic species they 

 may be present in large numbers without doing any injury 

 whatsoever, except to render the milk less palatable by making 

 it sour. 



The problem of supplying our great cities with milk has be- 

 come a difficult one with their increasing growth. Milk must 

 be drawn from a wider and wider territory, involving a more 

 and more extensive use of railroads. For New York some 

 of the milk comes from a distance of 500 miles. This problem 



