CHAPTER XV. 



THE BACTERIOLOGY OF FOODS. 



THE relation of bacteria to foods is an important one and 

 should be as thoroughly understood as possible by both the 

 profession and the laity. The relationship may be expressed 

 thus: 



I. Foods serve as vehicles by which infectious agents are 

 conveyed to the body. 



II. Foods are chemically changed and made unfit for use 

 by the bacteria. 



I. Foods as Fomites. In animal food the first source of 

 infection is the animal itself, danger of infection always 

 accompanying the employment of foods derived from dis- 

 eased animals. Thus, milk apparently normal in appear- 

 ance has been found to contain dangerous pathogenic bac- 

 teria. The tubercle bacillus is one of the most important of 

 these, and at the present time the consensus of opinion in- 

 clines toward the view that the great prevalence of tubercu- 

 losis among human beings depends partly upon the inges- 

 tion of tubercle bacilli in milk. It does not appear necessary 

 that the udder of the cow be diseased in order that the or- 

 ganisms enter the milk, as they seem to have been found in 

 milks derived from cows whose udders were entirely free 

 from demonstrable tuberculosis. It is, therefore, impera- 

 tive to retain only healthy cows in the dairy, and careful 

 legislation should provide for the detection and destruction 

 of all tuberculous animals. The detection of tubercle bacilli 

 in milk can only be certainly accomplished by the injection 

 of a few cubic centimeters of the fluid into guinea-pigs and 

 noting the results. 



In addition to the tubercle bacillus, pyogenic streptococci 

 have been observed in enormous quantities and almost pure 

 culture in milk drawn from cows suffering from mastitis, 

 Stokes * has observed a remarkable case of this kind in which 

 the milk contained so much pus that it floated upon the top 



* "Maryland Medical Journal," Jan. 9, 1897. 

 296 



