98 MILK 



the amount of external pollution which has been added to milk 

 from an estimation of the number of bacteria in chance samples 

 of vended milk. 



The determination of the number of B.coli and allied organisms 



o 



is a much more valuable estimation. These organisms as shown 

 in Chapter I are extremely abundant in cowdung, and although 

 there are other sources of milk contamination undoubtedly 

 manurial pollution is by far the most prevalent. These bacilli 

 are absent from milk samples collected directly from the teats 

 or under conditions of great cleanliness. Further they can be 

 easily isolated and numerically estimated by methods which are 

 likely to give the same results with different workers. 



As regards samples collected at the byre there is no doubt 

 that this estimation is a direct and extremely valuable method 

 of measuring the degree and extent of manurial contamination. 



The value of this enumeration for chance samples of ordinary 

 vended milk involves matters of great complexity, and it is a 

 problem of great difficulty to correctly gauge the significance of 

 these bacilli. If it were a practicable and universally adopted 

 procedure to thoroughly cool milk after collection, and then to 

 maintain it until sold at a temperature so low that B. coli will 

 not multiply in it, any standards framed for B. coli in byre milk 

 would be equally applicable to milk as sold. Under present 

 conditions this is by no means the case, and it becomes a very 

 complicated problem to say what number of B. coli may be 

 allowed in vended milk samples as sold under present-day con- 

 ditions. 



In the writer's opinion the most reliable deductions can be 

 obtained from a study of the rate of multiplication of B. coli 

 in milk under different conditions of temperature, etc. From 

 his investigations in this direction 1 he is of opinion that while 

 samples at the byre should not contain more than one B. coli 

 (including allied organisms) per c.c., samples of milk as vended 

 should not contain more than 100 to 500 in winter and 1000 to 

 2500 in summer as extreme permissible limits. 



The estimation of the number of spores of B. enteritidis 

 sporogenes is also of considerable value more particularly because 

 1 Ideal Government Board ', Medical Officer's Report 1909-10, p. 474. 



