GERMS IN RELATION TO MILK 7 



repeated at frequent intervals. Milk treated by continued, inter- 

 mittent heating at 140 F. has been kept for years without chang- 

 ing, owing to the destruction of germs (and ferments) in it. As 

 the time required for the destruction of germs at this temperature 

 Is too great for commercial purposes, temperatures ranging from 

 160 to 176 F. are usually applied for either killing or checking 

 the development of germs in milk. Heating milk below the boiling 

 point with this object in view is called technically pasteurization, 

 after the great originator of the process. If properly done, pasteur- 

 ization kills most of the germs in milk (95 to 98% of all bacteria, 

 including those which cause disease in the human most commonly, 

 i. e., the miscellaneous and undetermined germs which induce diar- 

 rheal diseases in infants, and the special germs of typhoid and scarlet 

 fever, malta fever, tuberculosis, and diphtheria), and this is the best 

 way to obviate the dangers of dirty milk for human consumption — 

 more particularly in the case of infants. The spores of germs — 

 the immature forms from which germs develop — are not killed by 

 pasteurization or even by boiling milk ; a still higher temperature 

 is required. Most milk contains some spore-bearing germs and so 

 cannot be made absolutely germ-free by pasteurization or boiling. 

 Boiling milk alters its taste and chemical composition, and renders 

 it somewhat less digestible. There are certain drawbacks to pas- 

 teurization, however. If the milk has been kept long before heat- 

 ing, poisons may form in it which the heat will not destroy. 



Our knowledge concerning these poisons (or, more techn callv, 

 toxins) resulting from the growth of germs is very slight. That is, 

 concerning the varieties of germs which may produce toxins in milk, 

 and the harm which they do, and the effect of heat upon them. It 

 is generally conceded, however, that it is impossible to make an old 

 and dirty milk harmless by heating it, and that myriads of dead 

 bodies of germs and their products are sometimes poisonous to 

 infants — even after the milk containing them has been pasteurized. 

 Milk, then, which contains a large number of germs, or an acidity 



