MICRO-ORGANISMS IN MILK 263 



The writer found in Chicago in 108 samples of raw milk 

 4,804,300 bacteria per cubic centimeter, and r 1,772, 100 in 107 

 samples of pasteurized milk. 



If milk were a transparent fluid like water these enormous 

 numbers would render it turbid, and we would hesitate to con- 

 sume as food a substance of such appearance. 



These figures do not, however, adequately represent condi- 

 tions as they exist at the present time. Pasteurization of milk 

 has greatly increased, especially in large communities, and the 

 number of bacteria is materially reduced by this process. Fur- 

 thermore, the methods of production have improved, and milk 

 with relatively small numbers of bacteria is not as uncommon 

 today as formerly. It should also be remembered that numbers 

 of bacteria in milk as published are not obtained by uniform 

 methods, so that the results are by no means comparable. How- 

 ever, the fact remains that in communities where chiefly raw 

 milk is consumed the bacterial pollution is relatively heavy. 



As stated before, the great majority of micro-organisms de- 

 tected in milk are harmless, but not infrequently the germs of 

 infectious diseases gain access. Epidemics of typhoid fever, 

 diphtheria, scarlet fever, sore throat, and other diseases have been 

 traced to infected milk-supplies. It has been shown further that 

 milk infected with bovine tubercle bacilli is not infrequently the 

 cause of tuberculosis in children, and such milk is only too com- 

 mon. Probably in all municipalities where raw milk is sold some 

 of it is infected with tubercle bacilli. 



The virus of the diseases mentioned gains access to milk 

 through human carriers or infected animals. And we know fur- 

 thermore that some disease germs are able to multiply in milk at 

 an enormous rate when the temperature of the milk is favorable. 

 Even at 15 C., a temperature not at all uncommon in market milk, 

 there may be multiplication of some disease germs. 



On the other hand, germs may be useful by their action on 

 the constituents of milk. Buttermilk, for example, may contain 

 500,000,000 to 1,000,000,000 bacteria per cubic centimeter; the 

 flavor of butter is largely dependent upon the kinds of bacteria 

 active in the ripening of cream ; and the aroma and digestibility of 

 cheese are the result of the action of bacteria and molds. None of 

 these dairy products can be successfully produced from sterile 

 milk, or even from milk containing a relatively small number of 

 bacteria, unless the necessary organisms are inoculated, but as our 

 knowledge of the bacteria that produce desirable flavors in dairy 

 products grows, it becomes more feasible and more desirable to 

 use only clean and pasteurized milk for manufacture of cheese, 

 butter, and other dairy products. This is the more important, 



