MILTON J. ROSENAU 407 



Yersin, who in 1888 used tapering test tubes. The capillary tubes used by Foster, the 

 sealed test tubes used by Theobald Smith and others, and the sealed boxes used by 

 Bang and others gave effective protection against air. McFadyen and Hewlett used a 

 closed lead coil submerged in a water bath through which the infected milk was passed. 

 This method was elaborated in detail in the technique used by North and Park in their 

 recent work. By this method the cooling effect of air, pellicle, serum, and froth for- 

 mation are avoided. The pasteurization of milk in glass bottles, such as baby bottles 

 and ordinary milk bottles, has often been advocated, but the air space at the top of 

 such bottles makes possible the formation of pellicle, scum, and froth, which is a 

 refuge to the bacilli, unless the air itself is also heated sufficiently. 



Traum and Hart' took advantage of an opportunity to test the effect of heat on 

 naturally infected milk pasteurized imder commercial conditions such as prevail to- 

 day in all modern city milk plants. Milk was obtained from a herd of five hundred 

 cattle, all of which were tuberculous, and the milk of which was allowed to be sold 

 after it had been pasteurized. It was found that 140"^ F. for twenty minutes killed 

 all the tubercle bacilli in the milk. In a later article and as a result of further work, 

 Traum concludes that pasteurization at a temperature of not less than 142° F., and 

 for a period of not less than thirty minutes, as required by most health departments 

 at present, should be effective in destroying tubercle bacilH which may be present in 

 the milk. Such exposure leaves a good margin of safety. 



The experiments of a group of bacteriologists working at Endicott (N. Y.) in 

 1922-23, the results of which were reported in the United States Public Health Service 

 Bulletin 147, gave special attention to temperatures lower than 140° F. for a period of 

 thirty minutes with commercial machines. Their conclusions were based upon a large 

 volume of data. A total of 718 samples were tested on 1,436 guinea pigs by Moore, 

 Park, Rosenau, Wadsworth, Armstrong, and North, who found that under practical 

 conditions the tubercle bacillus is killed at 138° F. in thirty minutes. 



This conclusion has been attacked on the ground that the experimental data in 

 the report were insufficient. North and Park therefore carried this work a step far- 

 ther, using the closed-lead-coil system. They made a total of fifteen separate tests 

 at twelve different temperatures between 170° and and 130° F., and found that tuber- 

 cle bacilH were killed at 136° F. in thirty minutes. This constitutes the most extensive 

 series of experiments ever made to determine this point, and the careful work carries 

 conviction. Chart II summarizes this work. 



It can therefore be asserted with confidence that it has been amply demonstrated 

 that 140° F. is more than enough to kill tubercle bacilli; in fact, they succumb at 

 136° F. in thirty minutes. 



TIME AND TEMPERATURE OF PASTEURIZATION 



It has been abundantly demonstrated that heating milk to 140° F. (60° C.) for 

 twenty minutes is more than sufficient to kill the bacilli of tuberculosis, typhoid fever, 

 paratyphoid fevers, dysenteries, and diphtheria; the streptococci of scarlet fever and 

 septic sore throat; the micrococcus of Malta fever; the virus of foot-and-mouth dis- 

 ease; and all other non-spore-bearing, milk-borne infections that are of concern to 



• Traum, J., and Hart, G. H.: /. Am. Vet. M. A. Aug., 1916. 



