346 STATE BOARD OF AGRICULTURE 



KILLING THE TUBEEOLE BACILLUS IN MILK. 



BY CHARLES E. MARSHALL. 



Bulletin 173. — Bacteriological Department. 



Led to this work by expressions of doubt concerning the value of pasteurization 

 when the bacillus tuberculosis is in question, I have attempted to present in a brief 

 way a limited review of a few experiments made by others and some carried on at 

 this laboratory, in order that the readers of Experiment Station bulletins may form 

 a reliable judg-ment and may guard against danger. Pasteurization for other pur- 

 poses than killing the tubercle bacillus will not form a part of this treatise. For a 

 general consideration of pasteurization and its objects, bulletins Nos 133 and 147 

 , may be consulted. 



Whether milk ever contains the tubercle bacillus or not will not be discussed; the 

 conclusions of eminent experimenters will be assumed as beyond contradiction that 

 the tubercle bacillus is found in milk from tuberculous cows in no small per cent of 

 cases. Such milk has been demonstrated to be infectious upon lower animals; and 

 in the case of man, which direct demonstration is precluded, indirect evidence has 

 been adduced which has established the relation of known tuberculously infec- 

 tious milk to certain eases of human tuberculosis almost beyond a doubt. In a 

 future bulletin, tuberculous milk and its infectious nature will be treated in detail. 



Woodhead has made extensive experiments with the tubercle bacillus to ascertain 

 a safe method to render it innocuous in milk. One statement which he makes has 

 much significance when possible tuberculous infection is in dispute. He says "milk 

 from tuberculous udders is in all cases possessed of the power of setting up tubercu- 

 lous infection." This opinion will designate the true position of Woodhead from 

 whom valuable work and suggestious will be quoted. "It was found," he says, 

 "that the exposure of even virulent tuberculous milk to a temperature of 85° O. 

 (185° F.) for five minutes is sufficient to render it innocuous, altliough the same 

 material brought rapidly to a temperature of 90° C. (194° F.) still retains some 

 power of infection. 



The following detailed result of Woodhead may be given to advantage, both in 

 interest and in their practical bearing: 



"Positive result momentarily heating QCC. (194° F.) 

 22min. " at 75°C. (167 "F.) 



30 min. " at 70°C. (158* F). 



3 hrs. " at 65°C. (149° F.) 



12 hrs. " at 60°C. (140° F.) 



Heating longer than this rendered the germs innociious by inoculation." 

 [By "positive results," — inoculation tests were made upon lower animals with 

 some of the milk after treatment to determine whether the milk was still infected 

 or not. If an animal succumbed to tuberculosis, he, Woodhead regarded the result 

 as positive. — Author.] 



In another experiment the tuberculosis material was heated to different tempera- 

 tures for various periods of time, and then fed to pigs. This is illustrated as 

 below: 



