236 MILK AND THE PUBLIC HEALTH CHAP. 



virulence test is not considered essential their presence can 

 be readily determined. In particular, B. enteritidis sporogenes 

 is an organism which does not multiply in milk, so that 

 this determination should be especially valuable for vended 

 milk. On the other hand, there is some doubt as to how far 

 this bacillus may gain access to milk from other than man- 

 urial sources, and these, although undesirable, may be less 

 prejudicial than direct manurial pollution. The spores, being 

 highly resistant, may live for very long periods. 



The ordinary method of examination is not sufficiently 

 sensitive, and a more delicate method of enumeration, such as 

 the one described on p. 189, must be used if this enumeration 

 is to be of value. There is also a possible error due to 

 unequal distribution of the spores and irregularities of 

 sampling. Further experiments as to the value of this 

 test are required. 



As regards definite standards, any adopted are equally 

 applicable to byre and vended milk, and for all times of the 

 year. 



EXAMINATION OF STAINED CENTRIFUGALISED DEPOSIT 



This is a procedure which is very readily carried out, while 

 the results are available without delay. It enables unknown 

 milk samples to be divided into those which are recently 

 collected and those which are either stale, or if fresh, then 

 collected under conditions of gross bacterial contamination. 

 With care a rough but useful opinion can be obtained from 

 the stained deposit as to the probable number of bacteria 

 present. 



Considering all the different procedures, the writer is of 

 opinion that the most reliable estimate as to the bacteriological 

 condition of a given milk sample, and the cleanliness con- 

 ditions under which it has been collected, can be arrived at 

 from the enumeration of B. coli and allied organisms, number 

 of spores of B. enteritidis sporogenes, and examination of the 

 stained centrifugalised deposit. 



The other procedures add very little to the information 

 obtained from these three tests. 



