EXPERIMENT STATION BULLETINS 349 



explaining an apparently contradictory situation, such as lias been presented in the 

 review given. 



This bulletin does not pretend to solve the question that has been raised by the 

 review and discussion so far. but rather to contribute its share in the work re- 

 quired of many workers before our knowledge shall be adequate to safely reach 

 conclusions. 



In the past, all pasteurizing done at this station has conformed to one standard. 

 Tlie milk, after it has reached <iS° C. (1.5.5° P.). has been held for twenty minutes 

 at this temperature, and then cooled as quickly as possible. Bringing the milk up 

 to 68° C. (155° F.) requires some time, the length of which is dependent upon the 

 amount of milk and water, also upon the strength of the flame. No direct experi- 

 ments have been made until now to ascertain whether this method of pasteurization 

 would render milk safe from the action of the tubercle bacillus, should it be pres- 

 ent. 



In each experiment 10 c. c. of milk was used. It was sterilized and then allowed 

 to cool. Tuberculous material was then added and thoroughly macerated in it until 

 evidences of tuberculous material could be detected in its consistency. Before sub- 

 jecting this mixture to pasteurization, guinea pigs were inoculated with it to test 

 its virulence. It was then ijasteurized as described above, that is, as soon as the 

 temperature reached 68° C. (1.55° F.), it was held at that point for twenty minutes 

 and then cooled as quickly as possible. After the pasteurization, guinea pigs were 

 inoculated Avith this pasteurized mixture, to determine whether the tubercle bacil- 

 lus was dead. 



For each experiment, tuberculous material was obtained from a different source. 

 The object of this was to test the durability of tubercle bacilli coming from differ- 

 ent sources and presumably existing under somewhat different conditions, and 

 perhaps in different forms. In every case the material came from tuberculous 

 cows which were killed in an advanced stage of tuberculosis or had died of that 

 disease. Such, we believe, is the material which would naturally find its way into 

 milk. No effort was taken to secure tubercles in the incipient stages of growth or 

 in the most advanced, but rather to take parts of several in all stages of develop- 

 ment. 



The tuberculously infected milk was placed in a shalloAV dish for pasteurization. 

 The thickness of the layer of the milk in the dish could not have been over one 

 quarter of an inch. This allowed ready transmission of heat, so that one part of 

 the milk would not be one temperature and another part higher or lower. The dish 

 was placed in the bottom of a pail sterilizer and this placed on a water bath. This 

 pail sterilizer is described by Novy in Cent. f. Bakt. Bd. xxii. S. 340. Heat was ap- 

 plied under the water until the temperature registered 68° C. (155° F.) in all parts 

 of the vapor chamber. By means of a Reichert's thermo-regulator, this tempera- 

 ture was maintained constantly for twenty minutes. 



The inoculations of guinea pigs before and after pasteurization with the results 

 will be detailed below: — 



Experiment 1. Guinea pig, No. 44, was inoculated intra-abdominally with 1 c. c. 

 of the tuberculously infected milk before it was pasteurized. 



This animal died of general tuberculosis ten weeks later. Lungs, liver, spleen, 

 lynipliatic glands and peritoneum were seriously affected with the disease. 



Guinea pigs, Nos. 41, 42 and 43, were each injected intra-abdominally with 5 c. c. 

 of the same milk as used in the case of No. 44 after it had been pasteurized. 



At no time did any of these animals show symptoms of the disease either by ap- 

 pearance or by weight. They were all chloroformed when No. 44 died, but traces 

 of tuberculosis could not be found upon careful examination. 



Experiment 2. Guinea pig. No. 75, was injected intra-abdominally with 1 c. c. of 

 tuberculouslj^ infected milk, before it had been pasteurized. The tuberculous ma- 

 terial in this experiment was obtained from another animal. 



Four weeks later the pig became so emaciated and sick that is was chloro- 

 formed. Upon post mortem, the lungs, liver, spleen and lymphatic glands were 

 highly affected with the disease. 



Guinea pigs, Nos. 76, 77 and 78 were each injected intra-abdominally with 5 c. c. 

 of the same milk used for No. 75 after it had been pasteurized. They were all 

 chloroformed at the same' time that No. 75 was examined, but careful examination 

 revealed no lesions of tuberculosis. 



Experiment 3. Guinea pig, No. 127, was inoculated intra-abdominally with 1 c. c. 

 of tuberculously infected milk before undergoing pasteurization. The tuberculous 

 material used in this experiment came from a different source than in the two 

 previous experiments. 



