MILK-BORNE INFECTIONS 435 



that pathogenic germs are deposited in the milk under these con- 

 ditions. 



A bottle of milk left unprotected outside of the house may 

 furnish flies with the means of communicating disease virus, since 

 frequently a few drops of milk remain on the surface of the bottle 

 cap. A simple box to hold the milk will prevent this menace. 



4. Dust. Although infections through dust are considered 

 relatively scarce, the possibility of its communicating pathogenic 

 germs to milk cannot be entirely excluded. If, for example, there 

 is a case of typhoid fever in the family of a milk producer, and 

 the dejecta are left near a dairy barn or a milk house, the dust 

 may soon carry germs to the milk. It has been shown that ty- 

 phoid bacilli may live for weeks and even months under such con- 

 ditions, and in the soil for more than a year. Human dejecta, 

 therefore, should never be used for manuring. 



5. Domestic Animals. The careless habit of leaving bottles 

 of milk outside the house without protection exposes them to 

 visits from cats and dogs. Both animals may carry diphtheria 

 germs and the germs of other diseases, and by licking the caps of 

 milk bottles leave the germs which finally find their way into the 

 milk. 



6. The Cow. Finally, infection may be derived from the cow. 

 Of chief importance is the transmission of bovine tuberculosis 

 through milk. That bovine tubercle bacilli are infectious for man, 

 especially during infancy, is not questioned, and many investiga- 

 tions have shown that a considerable proportion of raw market 

 milk harbors living bovine tubercle bacilli. They reach the milk 

 either from a diseased animal directly when the udder is affected, 

 or through the dust from the dejecta of tuberculous animals. 



It is clear that milk and cream are exposed to infection at 

 many points, and the problem of prevention is proportionately 

 difficult. Methods of prevention are studied chiefly by investi- 

 gators of epidemics by definitely locating the source of infection. 



As previously stated, milk-borne epidemics are studied suc- 

 cessfully only by epidemiologic methods, while the isolation of a 

 specific disease germ, though desirable, is difficult and not alto- 

 gether necessary. The epidemiologist will attempt to tabulate 

 all cases of the disease and make inquiries as to the water and 

 milk-supplies of the stricken families, the exact date of the out- 

 break of the disease, and similar points of interest. Trask gives 

 the following points to be ascertained in the investigation of milk- 

 borne epidemics: 



"1. The number of cases of the disease existing in the involved 

 territory during the time covered by the epidemic. 



"2. The number of houses invaded by the disease. 



