42 MASTITIS OF THE COW 



In milk bacteria grow without changing the medium." 



In sugar media (glucose, maltose, lactose, saccharose) 

 no gas but a slight quantity of acid is formed so that the 

 media can contain 1-2 per cent, normal acid. 



Resistancy. — Streptococci are very sensitive. Usually 

 daylight will destroy a culture in a day. In stab cultures 

 or in blood in hermetically sealed capillary pipettes, kept 

 from the light, the organism may hve for 3-4 months. 

 Highly virulent streptococci appear to be more sensitive 

 and less vigorous than those of less virulence. 



Pathogenicity. — The virulence fluctuates greatly. 

 There are pathogenic streptococci which produce no lesions 

 in experimental animals, others which induce local lesions 

 only, and still others which cause death in variable lengths 

 of time. The vinilence can be raised by passage through 

 animals.^ 



Mice are the most susceptible to the infection. One 

 drop of bouillon culture subcutaneously can kill a mouse 

 in from 1 to 7 days or sometimes longer, 14 to 21 days, 

 depending upon the virulence. 



Autopsy. — If death occurs suddenly one perceives a 

 slight spleen swelling, and the point of inoculation is either 



^ As a rule, the literature states that the pathogenic strepto- 

 cocci coagulate milk quickly. This is insistently stated, especially 

 with reference to mastitic streptococci. Of nine different strains 

 of streptococci which I studied in this respect, of which seven were 

 mastitic streptococci, only one strain coagulated milk. This strain 

 was isolated in summer from a one-day-old milk sample; I had 

 undoubtedly isolated the lactic acid streptococcus instead of a 

 pathogenic streptococcus. 



The mistake in the literature mentioned probably rests upon 

 this fact, since the lactic acid streptococcus is a very common 

 saprophyte. 



^ The literature states that mastitic streptococci are never 

 pathogenic for small experimental animals, which is often, but not 

 always, the case. 



