500 QUANTITATIVE ESTIMATION OF BACTERIA IN MILK 



All the circumstances must be taken into consideration, including the 

 condition of the farms, the presence of preservatives, and the species 

 of the bacteria." 



Weigmann, in Sommerf eld's Manual on Milk, says : "Reports as 

 to the number of germs in milk naturally are very variable; they 

 simply indicate up to the present time that the bacterial contents are 

 occasionally very high. This in most cases is not of as bad a signifi- 

 cance as the figures make it appear. However, such figures gener- 

 ally point to an unclean method of obtaining the milk, and this will 

 betray itself generally by the presence of a larger amount of dirt or 

 they point to a not very careful or not rational method of treating 

 the milk." 



Conn's opinion is expressed as follows: "It is probably impossible 

 to fix upon any standard as to the number of bacteria which whole- 

 some milk may contain. Should we condemn milk when it has 10,000 

 per c.c. or 30,000 or 1,000,000 bacteria? To fix a standard is difficult, 

 because the number is so dependent upon the temperature and the 

 season of the year. . . . Sometimes this number (of bacteria in 

 special milk) has been fixed at 10,000, in other cases at 30,000. This 

 is practicable for small dairies where the dealer wishes to furnish 

 a special product at a special price, and where the dairy is within 

 a short distance of the consumer. . . . But for the general 

 milk supply of a large city it has, up to the present time, been found 

 quite impracticable to suggest any bacteriological standard without 

 excluding too large a portion of the milk which will be brought into 

 the city. Moreover, it seems by no means sure that such a standard 

 would be of much practical value, because even though the number 

 be large the milk may be perfectly wholesome if they are of the 

 normal lactic type; whereas a much smaller number of bacteria in 

 another sample of milk might make it decidedly injurious if the 

 bacteria should be of a different character. 



"These various facts raise the question whether a bacteriological 

 analysis which shall differentiate the different kinds of bacteria from 

 each other is possible and practical. Is it possible to devise some 

 means of analysis of the bacteria in milk which shall give the numbers 

 of the different kinds of bacteria, separating the normal forms from 

 those that render the milk suspicious? If we could do this, the 

 practical analysis of city milk might be more useful and might become 

 an efficient means in the hands of boards of health in protecting the 

 public from the dangers in its milk supply. There has hitherto been 

 no attempt made to develop such a method of differential analysis of 

 milk, and, indeed, at the present time we know too little in regard to 

 the relations of the different species of bacteria to the wholesomeness 

 of milk to make an analysis absolutely reliable." 



Jensen expresses himself as follows concerning this question: 

 "Of course, the number of bacteria in market milk varies greatly 

 according to its care and to the temperature of the air. Experience 



