545 STATE BOARD OF AGRICULTURE. 



sistant than those from the mouth of the cow and from cow feces but 

 less resistant than those from milk and cream. One strain upon which 

 special work was done was not affected by a temperature of 150° F. for 

 thirty minutes, at 1G0° F. from 53 to 99 percent of the individuals in 

 the culture succumb and at 165° F. all were killed. These same authors 

 (4) in a study of one hundred and seventy-four strains of colon bacilli 

 state that in 'milk a temperature of 115° F. for thirty minutes caused 

 the death of 93.02 percent of the strains and that all were killed at 150° 

 F. The results from repeated determinations of the thermal death 

 ]K)int of a given strain was observed to vai-y considerably. They con- 

 clude that, from their work, colon bacilli should not be expected in 

 milk pasteurized at 150° F. for thirty minutes. 



Working with Bact. tuberculosis, Theobald Smith (20) states that 

 the tubercle bacilli suspended in distilled water, in normal salt solution, 

 in bouillon or in milk are destroyed at G0° C. in fifteen to twenty minutes; 

 Avhile those on the surface of milk surrounded by the pellicle which 

 forms during the exposure may be found alive after an exposure at G0° 

 C. for sixt}^ minutes. A micrococcus was isolated from pasteurized 

 milk by Kussell and Hastings (17) who tabulate data showing that its 

 thermal death point in bouillon is 7G° C. and in milk and whey is 77° 

 C. Eussell and Hastings (IS) give data demonstrating that the thermal 

 death point of a micrococcus in milk when determined in an open vessel 

 is about 8° C. higher than when determined in sealed tubes. This differ- 

 ence they show to be due to the surface pellicle which formed on the milk 

 during exDOsure. Thev conclude that the destruction of bacteria in 

 milk by means of heat depends upon the conditions under which the 

 exposure is made; the formation of a pellicle protects any organism 

 within the pellicle. This protection is thought to be due largely to a 

 lower temperature at the surface and to the nature of the membrane 

 itself. In studying heat resisting strains of B. Coli, Zelenki (21) states 

 that their thermal death point is higher in milk than in bouillon and 

 suggests that the protein and fat are responsible for the protection. 

 Barthel and Stenstrom (5) conclude that the cells of Bact. tuhercidosis 

 in whey are killed by heating to 80° C. providing the large lumps of 

 coagulated casein have been removed by passing through a hair sieve — 

 the small flakes which pass through the sieve are without effect. Rosen- 

 gren (15) concludes from his data that bacteria are better protected 

 against a higli degree of temperature in raw milk than in milk sterilized 

 by heat. Bartlett and Kinne (G) suspended the spores of B. suhtiUs, Bact. 

 anthracis and B. vitalis in water, in glycerin, in olive oil, in cottonseed 

 oil and in paraffin and subjected them to various degree of heat. They 

 observed that in an autoclave under fifteen pounds pressure the spores 

 of B. vitalis suspended in water were killed within fifteen minutes; but, 

 when suspended in glycerin and in oil exposures for ninety minutes and 

 two hours respectively were required. Hammer (9, p. 32) states that 

 his unpublished data indicate that the acidity present in cream has an 

 important influence on the destruction of the Bact. lactis acicli forms by 

 heat. It is stated by Wolff (23, pp. GGG-G75, 737 and 711) that Bact. 

 gUntheri {Bad. lactis acidi) in sterilized milk, in bouillon and in water 

 was killed within twenty minutes at 70° C. but tliat in raw milk mem- 

 bers, of this group survive for half an hour at 70° C. or for fifteen 

 minutes at 80° C. He concludes that the protection is due to the forma- 



