324 MILK AND DISEASE 



consumptive milkers may sometimes be responsible for 

 the infection of the milk. 



It is only to be expected that butter, cheese, and 

 other dairy products prepared from unsterilized milk or 

 cream will not infrequently contain tubercle bacillus : 

 such has been found to be the case by many different 

 workers. Moreover, the organism may live in milk for 

 several months, and in cheese for a year or more. 



To avoid danger from these sources it is advisable, 

 wherever possible, to manufacture dairy products only 

 from milk or cream which 'have been pasteurized. 



Bacillus tuberculosis (R. Koch), is a very variable organism. 

 It is non-motile, usually rod-shaped, from 3 to 5 & long, . 5 /* broad, 

 sometimes curved, and in old cultures frequently appears in the 

 form of branching threads. 



In stained specimens a number of unstained vacuole-like 

 portions are usually seen. 



It stains easily with carbol-fuchsin and the stain is " acid-fast " 

 i.e. it is not decolourized by 25 per cent, sulphuric or 30 per 

 cent, nitric acids : it also stains by Gram's method. 



The bacillus is aerobic, and thrives best at 37 C. Its 

 thermal death-point is of great importance in regard to the destruc- 

 tion of living organisms in milk by the process of pasteurization. 

 Many experiments have shown that temperatures of 60 C. 

 maintained for twenty minutes, 65 C. for fifteen minutes, or 

 70 C. for ten minutes, are usually sufficient to destroy it, but 

 Bang considers that nothing less than 85 C., kept up for five 

 or ten minutes, suffices for absolutely reliable results. 



Direct sunlight destroys the bacillus very soon, and diffuse 

 daylight acts in a similar way but more slowly. 



A 5 per cent, solution of carbolic acid kills it in thirty to 

 sixty seconds, absolute alcohol in five minutes and a i in 

 1000 solution of mercuric chloride in ten minutes. 



