88 BACTERIOLOGY FOR NURSES 



pigment, such as B. prodigiosus or B. erythrogenes be present. 

 Blue milk is usually due to the presence of B. cyanogenes. Milk 

 colored by bacteria is apparently harmless. 



Pathogenic Organisms in Milk. There are two sources from 

 which disease-producing bacteria may gain access to milk : from 

 the cow, or from some human case. The latter is the much more 

 common. Bacteria causing typhoid fever, diphtheria, or scarlet 

 fever may find their way into the milk from carriers, convalescents, 

 or persons suffering from a mild form of the disease who are engaged 

 in handling the milk. Or infection may come in a less direct way : 

 contaminated water may be used for rinsing milk pails or flies 

 may convey the bacteria from excreta improperly disposed of. 



Of the diseases transmitted to man from the cow bovine tuber- 

 culosis and septic sore throat occur the most frequently. The 

 micrococcus causing Malta fever is usually conveyed by goats' 

 milk, although cows are said to be susceptible to the disease. Cases 

 of foot-and-mouth disease transmitted by milk are extremely rare. 



Just how the bovine tubercle bacilli find their way into the milk 

 supply has long been a question of intense interest. In the case 

 of a tuberculous udder it is a simple matter. It has been suggested 

 that cows suffering from pulmonary tuberculosis may cough up 

 bacilli, swallow them, and then pass them in their feces. As 

 enormous numbers have sometimes been found in feces, and as 

 practically all market milk has been contaminated with manure 

 rubbed off from the flanks of the cow, it is reasonable to assume 

 that occasionally tubercle bacilli gain access to the milk in this 

 manner. 



For many years it has been thought that bacteria never pass 

 through the mammary gland unless there is a local lesion. Recent 

 experiments, however, tend to prove that in case of generalized 

 tuberculosis of the cow tubercle bacilli may pass into the milk 

 without any evidence of the udder being diseased. 



To what extent milk contaminated with bovine tubercle bacilli 

 is responsible for human tuberculosis is still an undecided question. 

 It is stated that in districts where the milk from tuberculous cows 

 is consumed the children are frequently found to suffer from 



