THE RELATION OF MICROORGANISMS TO MILK. 33! 



There is another class of disorders not so well defined as the above 

 but which are nevertheless of great importance from the standpoint of 

 public health, especially of young children and also to some extent of 

 adults. This group includes such disorders as infantile diarrhoea, summer 

 complaint, cholera infantum and other disorders of the digestive tract. 

 The organisms producing these troubles doubtless belong to the group 

 of putrefactive bacteria which come from filth. Some of the gas pro- 

 ducers and some of the peptonizers are probably responsible for these 

 troubles. Shiga isolated from a large number of cases of infant diarrhoea 

 a bacterium which he named Bad. dysenteric, but in general the specific 

 organisms responsible for these intestinal troubles are not well known. 

 Their importance, however, is shown by the relation of the germ content 

 of milk to infant mortality (See Fig. 80). 



BACTERIOLOGICAL ANALYSIS OF MILK. 



The development of our knowledge of the relation of bacteria to the 

 wholesomeness of foods has led to a study of the bacterial content of milk 

 as a means of determining its wholesomeness. The methods used for this 

 purpose have followed quite closely those of the water bacteriologists. 



PLATING METHOD. The early workers in milk bacteriology attempted to deter- 

 mine only the number of organisms in the milk. This was done by plating in nutrient 

 agar. From the results of this analysis they attempted to judge the sanitary quality of 

 the milk. By this method the number of colonies developing in the plates is assumed to 

 represent the germ content of the milk. It should be borne in mind that such counts 

 are only approximate and always less than the actual number of organisms in the given 

 sample of milk. Even if the best methods are employed it is not possible to determine 

 the exact number of bacteria in any lot of milk. 



THE DIRECT MICROSCOPIC METHOD. The plating method is expensive because of 

 the large amount of time and materials needed. It is not possible for one person to 

 handle a large number of samples at one time. In routine work in the city laboratories 

 this labor has been a serious drawback to this method. In order to decrease the 

 labor and give greater possibilities to the work Stewart devised a method by which the 

 bacterial condition of milk can be studied by direct microscopic examination. His 

 purpose was to determine only the species present, but later Slack developed the method 

 so that it Is now used in some cities for determining the approximate numbers and at 

 the same time the general species present in a given sample of milk. 



LEUCOCYTES. The microscopic examination of milk sediment revealed the fact 

 that freqently a sample would be found which showed the presence of leucocytes in 

 greater or less numbers. The presence of these cells was regarded as important because 



