32 INFECTIOUS MASTITIS 



nothing in their character to suggest causative agencies other 

 than microorganisms. The tissue changes involved in the 

 deposition of fibrous tissue and the abscess formation are 

 known as the results of infection and the inflammatory pro- 

 cesses following them. These affections are mentioned in this 

 connection simply because the accumulating evidence tends to 

 strengthen the working hypothesis that they are the result of 

 bacterial invasion. 



VI. 



i; 17. Infectious mastitis. Cattle suffer frequently from 

 an acute inflammation of the udder as the result apparently of 

 an invasion by a number of bacteria. The results of the inves- 

 tigation of this affection thus far reported suggest that the 

 form which is transmitted from animal to animal is caused bj^ 



a streptococcus. It is, however, 

 •••••., ,••«. difficult to distinguish between 



o : \ ^ this affection and those caused 



e 



\ •% oO by certain other bacteria. It 

 r ••«...••% ^ \ ^ ^ seems likely that many cases are 

 \ ^^ i *' • ^ ,•••••••* primarily brought about by me- 



^ '' ""^ *^o ••••••**>* * chanical injuries which render 



/ '^. / ^ possible the entrance into the 

 -Q I J fre-sh tissues of the bacteria of the 



^OQ V*"*^*** ...-, skin or of the milk ducts. Other 



•** m/ '^P "^^S^ cases mav be due to infection 



through the teat of bacteria capa- 

 FiG. 5. Streptococcus from a |^|g ^f producing, by means of 



case of infectious mastitis. , . , ,• 1 ^ ^i • 



their metabolic products, the in- 

 flammatory condition without a distinct injury to the mucous 

 membrane. The former view that there was a sphincter mus- 

 cle near the base of the teat which closed the duct sufficiently 

 to prevent the entrance of bacteria to the secreting portions of 

 the gland was not well founded upon anatomical facts (Fig. 6). 

 The acute and more chronic inflammatory affections of the 

 udder fall very naturally into two groups, namely : (i) those 

 in which the parenchyma is most affected and (2) those in 



