4o6 



THE BACTERIAL ASPECTS OF PASTEURIZATION 



(1901), McFadyen (1904), Rosenau (1908), Schorer (1912), Traum and Hart (1916), 

 Traum (1922), and others found that the tubercle bacillus will surely be killed if ex- 

 posed to 140° F/ (60° C.) for twenty minutes or less, and this has recently been con- 

 firmed by North, Park, Moore, Rosenau, Armstrong, Wadsworth, and Phelps' and 

 again by North and Park.^ 



There is nothing in all this work to indicate that the pure cultures are any less 

 resistant than the tubercle bacillus in tissue lesions. North and Park conclude that 





CHART II 



Thermal Death Curi/e or TVeEficLB Bac/lius 



PAsrsc/fi/7//^e SrAA/oA/?o Af^/" /bz-JO' 



/S 20 eS so 3S 40 



■fs so SS 60 65 70 



(A/ofiTH - Pa/7/C- /926) 



(From "Standards for Milk Pasteurization," Am. J . Ilyg-, 7, 147. 1927.) 



artificial cultures of bovine tubercle bacilli show the same resistance to heat as the 

 tubercle bacillus in naturally infected milk. 



To determine whether tubercle bacilli are alive or dead, it is necessary to inject 

 guinea pigs. The ordinary cultural and microscopical methods are not applicable. 

 Many of the errors in determining the thermal death-points of this micro-organism 

 were due in part to a misinterpretation of the lesions produced by dead tubercle ba- 

 cilli, and at times to pseudo-tubercles produced by other pathogenic micro-organisms. 



Many of the heating experiments were unreliable on account of imperfect tech- 

 nique, especially when open tubes or flasks were used. The first to realize this was 



' Most of the work on pasteurization is reported in the Fahrenheit scale, which is better suited to 

 this purpose because it deals with whole numbers. For convenience, the comparison between the 

 Fahrenheit and Centigrade scales at the temperatures in question are given on Chart II. 



- North, C. E., e{ al.: U.S. Pub. Health Bull. 14J. 1925. 



3 North, C. E., and Park, W. H.: Am. J. Ilyg., 7, 147. 1925. 



