236 



BACTERIA IN MILK AND MILK PRODUCTS 



It will be admitted that this table exhibits much in favour of 

 pasteurisation; yet the crucial test must ever be the effect upon 

 pathogenic bacteria. Fliigge has conducted a series of experiments 

 upon the destruction of bacteria in milk, and he states that a 

 temperature of 158 F. (70 C.) maintained for thirty minutes will 

 kill the specific organisms of tubercle, diphtheria, typhoid, and 

 cholera. MacFadyen and Hewlett have demonstrated,* by sudden 

 alternate heating and cooling, that 70 C. maintained for half a 

 minute is generally sufficient to kill suppurative organisms, and such 

 virulent types of pathogenic bacteria as B. diphtheria, B. typhosus, 

 and B. tuberculosis. 



Respecting the numerical diminution of microbes brought about 

 by pasteurisation and sterilisation respectively, we may take the 

 following series of experiments. Dr H. L. Russell f tabulates the 

 immediate results of pasteurisation as follows : 



As regards the later effect of the process, he states that in fifteen 

 samples of pasteurised milk examined from November to December, 

 nine of them revealed no organisms, or so few that they might 

 almost be regarded as sterile; in those samples examined after 

 January, the lowest number was 100 germs per c.c., while the average 

 was nearly 5000. With the pasteurised cream a similar condition 

 was to be observed. Other workers hold that from 95 to 99 per 

 cent, of all bacteria are removed by pasteurisation. 



Summary of Practical Control of Milk Supply 



Briefly, it may be said that the requirement is a pure milk supply, 

 that is : 



(1) A clean, whole milk, unsophisticated and without preserva- 

 tion; 



* Jenner Institute of Preventive Medicine (First Series Transactions). 

 f Centralblatt far Bakteriologie, etc., Abth. ii. 



