II THE SOURCES OF BACTERIA IN MILK 19 



Bergey ^ examined a number of samples of milk collected 

 separately from each of the four quarters of the udder. In 

 these samples the number of bacteria ranged from (32 per 

 cent of the samples) to 93,100 per c.c. Like Henderson he 

 found the prevailing bacteria to be staphylococci, streptococci, 

 and pseudo-diphtheria bacilli. Only about 10 per cent of 

 the samples contained over 5000 bacteria per c.c. 



In regard to the sources of these bacteria, their primary 

 origin is certainly from outside the teat. It seems to have 

 been established that after milking a column of milk remains 

 in the teat canal. In this milk column any bacteria introduced 

 through the teat orifice will find a suitable nidus for growth. 

 The bacteria extend up, infect the milk cistern, and ultimately 

 the ramifications of the milk tubes through the udder. 



There is obviously, however, a considerable selective action 

 exerted, since the organisms found are almost invariably 

 staphylococci, streptococci, and other forms of micrococci. The 

 evidence of this selective action was clearly shown in certain 

 experiments undertaken by the writer, in which the interior of 

 the teats of goats were inoculated with streptococci of human 

 and bovine origin. As a rule the infecting organisms died out 

 after a period of time, to be measured by weeks, although in 

 one case the infecting streptococcus persisted for the whole 

 duration of the experiment, a period of over seven months. The 

 streptococci of human origin, in general, died out more rapidly. 



2. IntJ'odiwed during the Milking Operation. — The bacteria 

 introduced during milking are derived from three sources, (a) 

 the coat, udder and teats of the cows ; (h) dust from the 

 milking shed and the clothes of the milker, and (c) derived 

 from the hands of the milker. 



(a) No person possessed of any bacteriological knowledge, 

 who is acquainted with cows as usually kept, will need con- 

 vincing that heavy bacterial pollution must result from this 

 source. It is very common, indeed in some districts quite the 

 usual thing, to find the hind-quarters of the cow caked and 

 plastered with partially dried manure. This is, of course, 

 particularly the case in wet weather. The udder and teats 

 of the cows do not show such gross manurial contamination, 

 but are frequently dirty and show evidence of dried manure. 



' Bulletin No. 135, Depart, of Agric. Pennsylvania, 1904. 



