SUMMARY OF CHAPTER XV 



ON THE PRESENCE IN MILK OF CERTAIN ORGANISMS LIABLE TO 

 CAUSE DISEASE, WITH NOTES ON MILK-BORNE EPIDEMICS 



IT is not intended here to accord any general consideration to 

 microbial diseases of the udder, but certain affections of this organ, 

 which can be classified together under the term mastitis or in- 

 flammatory conditions of the udder, are sufficiently common to 

 call for a short consideration. 



Mastitis may be either chronic or acute. It may be caused 

 by the presence of streptococci or of tubercle bacilli in the udder. 

 It has been shown in Chap. VII that the presence of streptococci 

 in milk cannot necessarily be regarded as pathological even when 

 present in milk obtained direct from the udder. Streptococci can 

 be found nearly everywhere, and have been shown to be present 

 on the outside of the udder and on the skin of the cow and to gain 

 access to the milk directly from this position. It is also possible 

 that they may find their way some distance up the teat and thus 

 be passed out with the first portions of milk. 



There is no doubt that a large number of cases of mastitis are 

 due to infection by streptococci. How far such strains of strepto- 

 cocci may be pathogenic for the human species has not as yet been 

 accurately determined, and it is likely that such a determination is 

 hardly possible. Much time and labour have been expended by 

 numerous observers in the endeavour to classify streptoccoci into 

 pathogenic and non-pathogenic strains. These efforts cannot, 

 however, be regarded as having been crowned with success. There 

 is evidence to show that a strain of streptococcus, which may be 

 apparently harmless, may become virulent as a result of being 

 grown upon different media, more especially by passage through 

 the animal organism. 1 



Examination of the general milk supply in a number of towns 

 has shown the wide prevalence of streptococci in samples of market 

 milk. In several cases where pathogenicity of these organisms was 

 tested on the lower animals a number of such strains were found 



1 Cp. Heinemann and others. 

 244 



