136 THE BACTERIAL CONTENT OF MILK 



Staphylococcus family multiply much more rapidly than do 

 the Streptococcus family ; the B. subtilis, which is almost ubiquitous 

 in its distribution and constantly occurring in milk, multiplies more 

 rapidly than the B. butyricus. Experiments for determining the 

 exact time of division of the Schizomycetes have been often made, 

 and though the results obtained differ according to conditions and 

 medium, we may take it that division of many of the common 

 bacilli will, as a rule, take place within thirty minutes. At this rate 

 in twenty-four hours one individual would give rise to many 

 millions of similar individuals. Many organisms, however, do not 

 multiply at this rate, and even this rate declines, owing to various 

 circumstances, as time passes. From a number of experiments 

 Klein calculated that for certain organisms the multiplication 

 during the first twenty-four hours is eighty thousand-fold, during 

 the second twenty-four hours four hundred-fold, and during the 

 third twenty-four hours five-fold.^ 



In the second place, we must revert to a remark made earlier 

 in the present chapter to the effect that there is no standard or 

 uniformity in the numerical estimation in milk. A large number 

 of observers have recorded widely-varying returns due in not a 

 little measure to the widely-varying conditions under which the 

 milk has been collected, stored, and examined. Nor is it possible 

 to establish any standard which may be accepted as a normal 

 or healthy number of bacteria, as in the case of water. Many 

 London milks would exceed 500,000 micro-organisms per c.c.^ 

 Until some common international standard is established, mathe- 

 matical computations are in reality practically worthless. They 

 are for one thing needlessly alarming and sensational. Moreover, 

 it should be remembered that, for comparative purposes, reliance 

 cannot always be placed upon these numerical estimations. They 

 vary from season to season, from day to day, and even from hour to 

 hour, depending upon a hundred varying conditions. Furthermore, 

 as we shall have occasion to point out at a later stage, large 

 numbers of bacteria are economic in the best sense of the term, 

 and the bacteria in milk are no exception to the rule. Large 

 numbers are not therefore necessarily an evil. 



Nor is it the number of organisms alone which is affected by 

 the temperature of the milk. There is abundant evidence, obtain- 



^ Stevenson and Murphy, Hygiene and Public Healthy vol. ii., p. 21. 



2 British Medical Journal^ 1895, vol. ii., p. 322. Bitter has suggested 

 5o,cxx) micro-organisms per c.c. as a maximum limit for milk intended for 

 human consumption. 



