INTER-RELATIONSHIP OF BACTERIA IN MILK 139 



" The inference to be drawn from these gross results is clear : 

 a certain proportion of the samples of milk contained bacteria 

 which, under favourable circumstances, gave to the milk noxious 

 properties, the development of which could be checked in many 

 cases by preventing the growth of these bacteria. The difference 

 between refrigerated and non-refrigerated milk would have been 

 ver}' much greater, if the milk had invariably been cooled immediately 

 after the milking of the cows" (Delepine). It should further be 

 noted that here also the influence of time must not be ignored, 

 for if the milk had been refrigerated immediately after milking, 

 the period which elapsed and during which there was multiplica- 

 tion of organisms and increase of toxicity would have been saved, 

 and thus less toxic substance would have been liberated in the 

 milk. 



The practical application of the effect of temperature has been 

 tersely expressed by Dr \V. H. Park, who states that " with only 

 moderate cleanliness, such as can be employed by any farmer 

 without adding appreciably to his expense, namely, clean pails, 

 straining cloths, cans or bottles, and hands, a fairly clean place 

 for milking and a decent condition of the cow's udder and the 

 adjacent belly, milk when first drawn will not average in hot 

 weather over 30,000 and in cold weather not over 25,000 bacteria 

 per c.c. Such milk, if cooled to and kept at 50' F., will not contain 

 at the end of twenty-four hours over 100,000 bacteria per c.c. If 

 kept at 40° F. the number of bacteria will not be over 100,000 

 after forty-eight hours." ^ 



By way of summary it may be said that to refrigerate milk 

 immediately after drawing it from the cow is to reduce the number 

 of bacteria and to diminish the potential toxicity of the milk. 



3. The Inter- relationship of Bacteria in Milk 



The third condition which controls the bacterial content of 

 milk now calls for attention. An obvious result of a great 

 increase in bacteria in a given quantity of milk is that the 

 competition becomes keener owing to the struggle for existence ; 

 so that a secondary effect of time and temperature is a diminu- 

 tion in number. But, what is perhaps of greater importance, it 

 appears that certain species become annihilated by the predomin- 

 ance of other more resistant or stronger species. Hence, at the 

 end of twenty-four hours — and we take that period as fairly repre- 



* Jour, of Hygiene, 1901, vol. L, No. 3, p. 401. 



