164 BACTERIA IN MILK 



on the particular combination of bacteria present. ' There is 

 considerable evidence that the occurrence of souring holds in 

 abeyance for a time the activity of putrefactive organisms whose 

 special characteristic is the disintegration of the proteid molecules. 

 Many changes, which may be denominated economic diseases of 

 milk, are due to bacteria, e.g., the occurrence of ropy milk, bitter 

 milk, and coloured milk. 



Pathogenic Organisms in Milk. — From the hygienic 

 standpoint the most important consideration is that of the 

 conditions under which organisms pathogenic to man gain access 

 to it. These may originate in diseased conditions occurring in 

 the cow, or the milk may become contaminated from cases of 

 human disease. With regard to the former, the two most 

 important are inflammatory and suppurative disease of the 

 udder, and tuberculosis. Amongst the organisms found in the 

 lacteal ducts are streptococci, and though frequently these are 

 harmless, unfortunately amongst them may be the streptococcus 

 pyogenes, and this may cause a streptococcal mastitis, sometimes 

 with abscess formation. The milk in such a case will contain 

 large numbers of streptococci; it may even contain pus and 

 blood-stained serum. There is too much evidence to show that 

 even such milk, and at any rate milk from less acute conditions, 

 finds its way into large milk supplies such as those sent to towns, 

 and definite outbreaks of streptococcal sore throat and abscess 

 in the cervical glands have actually been traced to such sources. 

 Probably many similar cases of a sporadic kind have a like 

 origin. 



Tuberculosis in the cow is, however, the most serious danger 

 arising from the consumption of milk. The relation of the 

 bovine type of the tubercle bacillus to the human is discussed 

 in Chapter X. Here it need only be said that where tubercular 

 disease occurs in the cow's udder, tubercle bacilli will be found 

 iu the milk, and, further, that where generalised tuberculosis 

 occurs in the animal, tubercle bacilli have been found in the 

 milk without evidence of the udder being diseased. The im- 

 portance of this observation is evident from the fact that a cow 

 containing enormous deposits of tubercle in the lungs and 

 peritoneum may to external inspection appear in prime condition. 

 Great controversy has taken place as to the prevalence of 

 tubercular disease in man traceable to the consumption of 

 tuberculous milk, and sometimes observations made by different 

 observers have appeared contradictory. In connection with this 

 subject it is necessary to bear in mind that the incidence of 

 tuberculosis in cattle, and consequently the incidence of bovine 



