370 HUMAN BIOLOGY 



season, but certainly unfavorable distinctions are fast 

 breaking down. 



However, in regard to fluid milk and fresh milk products, 

 the greater hazard of the distant city consumer has 

 demanded a degree of protection which has so far not been 

 equally available in the regions of milk production. 



The milk supply of cities in particular required and has 

 received more attention from the health authorities than any 

 other food. Milk has long been recognized as a possible 

 cause of disease, coming directly from the cow (e.g. bovine 

 tuberculosis and streptococcus sore throat where this is 

 due to an inflamed udder discharging pus in the milk) or 

 indirectly from the handler (e.g. typhoid fever, diphtheria, 

 septic sore throat, when this is due to sore throat in the 

 milker, etc.), and has in fact been a prohfic source of 

 epidemics. 



Of the 776 epidemic outbreaks of disease traced to milk 

 in the United States in recent years, as reported by Armstrong 

 and Parran of the United States Public Health Service, 

 613 were of typhoid fever, 7 of paratyphoid, 6 of dysentery 

 and diarrhea, 42 of septic sore throat, 6^ of scarlet fever 

 and 43 of diphtheria. Probably only a low percentage of 

 tuberculosis in humans (less than 5 per cent) is due to the 

 bovine tuberculosis conveyed by milk or its products. 



By pasteurization and central bacteriological control of 

 the milk supply, cities have learned to protect themselves 

 against the hazards of disease germs introduced into the 

 milk during its production or distribution. All forms of 

 pathogens 'likely to be found in milk are destroyed at a tem- 

 perature of 140° in twenty minutes. Commercial pasteuriza- 

 tion applies this treatment. Because of numerous possibilities 

 of milk escaping the full treatment intended, the equipment 

 must be carefully designed and operated. Legal definitions 

 of pasteurization differ. New York City requires 143° for 

 thirty minutes. At about 145° in thirty minutes definite 

 physical change begins, the fat globules become dispersed 

 and cream does not rise as completely. At higher temper- 

 atures a more definite chemical change occurs. 



Pasteurization is little practiced in the country and 

 small town. Here again isolation is a safeguard. Suppose 



