230 BACTERIA, YEASTS, AND MOLDS 



general question cannot be answered and it will always be a 

 matter for individual decision. That there is some danger 

 is certain. Whether the danger is sufficient to warrant 

 or demand the pasteurization of all ordinary market milk 

 is a matter of opinion upon which bacteriologists are not 

 yet agreed. For young children who must be fed upon 

 cow's milk it is, under the conditions of modern life, 

 not safe to use the ordinary milk supply. Many children 

 are brought up on such milk without suffering materially 

 therefrom ; but if it is used with young children there is 

 considerable danger of the diseases mentioned, especially 

 diarrheal troubles. In feeding young children, therefore, 

 it is wise, and almost necessary, to adopt some method, 

 preferably pasteurization, of destroying the disease germs 

 that may be present. ■ If the milk is to be used by adults, 

 the necessity is not so great, for adults are not as a rule 

 so liable to diseases from this source. Nevertheless milk 

 from the common milk supply, unless pasteurized, must 

 be looked upon as a possible source of typhoid fever and 

 some other troubles. It should be emphasized especially 

 that milk is not necessarily harmless because it has not 

 soured. It is true that soured milk contains more bacteria 

 than sweet milk, but most of them are harmless, while a 

 sample of milk that is perfectly sweet may contain disease 

 bacteria and be unsafe to use. 



The Air. The readiness with which bacteria can float 

 in the air suggests that they may be easily distributed by 

 this means. The agency of air in distributing diseases 

 has been somewhat overrated, but it occurs in a few dis- 

 eases which we usually look upon as extremely contagious. 

 Skin diseases, like ^measles, scarlet fever, and smallpox, are 



