540 



THE CONTROL OF THE MILK SUPPLY 



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 experi- 

 ments 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 

 fever, 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. diphtherice, B. typhosus, and B. tuberculosis.^ 



Respecting the numerical diminution of bacteria brought about 

 by pasteurisation and sterilisation respectively, we may take the 

 following two sets of experiments. Dr H. L. Russell ^ 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. 



Sterilisation, as a term, means that milk has been boiled, with 

 or without pressure, for a sufficient period of time to kill all. 

 bacteria and their spores. Probably only a small amount of 

 " sterilisation " reaches this standard. Nevertheless such is the 

 standard and it is obtainable in one of two ways ; either by heating 



' Jenner Institute of Preventive Medicine, Transactions (First series). 

 ^ See also Archives of Pediatrics, 1896 (August), R. G. Freeman. 

 •' Centralblatt fiir Bakteriologie, etc., 1 1 Abteilung. 



