EXPERIMENT STATION BULLETINS. 231 



Those bacteria which peptonize or digest the casein. 



3 6 9 29 30 33 38 43 44 45 46 48 60 



+ + + + + + + + + + — 



62 107 112 115 116 117 



— + — + + + 



Those bacteria which curdle then peptonize the casein. 



3 6 9 29 30 32 38 43 44 45 46 48 60 



+ + + ______ 



62 107 112 115 116 117 



- + - - + 



Those bacteria which produce an acid. 

 3 6 9 29 30 32 38 43 44 45 46 48 60 



62 107 112 115 116 117 



+ + + - - + 



Those bacteria which produce no perceptible change in milk. 

 3 6 9 29 30 32 38 43 44 45 46 48 60 



62 107 112 115 116 117 



+ 



4. The Investigation of the Thermal Death-Points of the 



Species Isolated. 



It is generally recognized that there are always left after Pasteuriza- 

 tion many resistant bacteria, and it has been suggested that by a mod- 

 erate elevation of the temperature, these might be killed. 



From a perusal of the thermal-death-points of the species isolated, it 

 will be easily seen that a slight elevation of temperature would have little 

 effect and that the temperature employed was sufficiently high to accom- 

 plish its purpose, if the pathogenic bacteria were also killed. 



A special experiment was made with the tubercle bacillus. Tuber- 

 culous material was taken from an animal affected with tuberculosis, 

 and was thoroughly mixed in milk. Part of the milk so treated was 

 heated at 68° C. for 20 minutes, then injected into guinea pigs, 3 in num- 

 ber; the other part was injected into a guinea pig without heating. 

 The three pigs did not contract tuberculosis while the one did. This 

 experiment will be reported in a bulletin on tuberculosis, but this is 

 sufficient to show that the heating at 68° C. for 20 minutes was fatal 

 to the bacillus. [This must not be considered conclusive. Author.] 



The following table will illustrate the resistance of the bacteria iso- 

 lated from Pasteurized milk. 



The temperatures are centigrade and the marks, plus denotes resist- 

 ance to the temperature and minus denotes killed at the temperature. 



