944 Veterinary Obstetrics 



The handling of parturient paresis by intra-mammary injection 

 is a fruitful source of mammitis, as already related while discuss- 

 ing that affection. 



Most infections of the body have been attributed to " taking 

 cold," and it is assumed that mammitis may be caused or its 

 establishment favored by exposure to cold, dampness or drafts. 

 Perhaps these factors do depress the system and favor the advent 

 of mammitis. 



Contusions exert an important inriuence by devitalizing the 

 tissues and rendering them more vulnerable to infection. Thus 

 a very pendent udder, buffetted back and forth between the legs 

 of a rapidly moving cow, may seriously contuse the gland and 

 destroy its normal power of resistance. A rough milker may 

 readily induce contusions of the udder which may do much to 

 cause mammitis. 



It is unnecessary for the infection to be introduced immedi- 

 ately from the outside. The teat orifice and lower part of the 

 cistern already contain, in the milk, some bacteria, usually of a 

 kind not pathogenic for the parts so long as the gland is not dis- 

 turbed. Whenever the gland is contused, or other accident occurs 

 to depress the vitality of the ti.ssues, the hitherto harmless (sap- 

 rophytic) bacteria, may become pathogenic. 



When the udder is overdistended, the tissues become weakened 

 and infection is favored. The whole udder projects very promi- 

 nently in the cow, and is accordingly exposed to injury. The 

 posterior teats are shorter than the anterior, are more rigid, and 

 are directed more or less backward in a direction which renders 

 them more susceptible to injury from pressure and from dirty 

 bedding-straws being pushed through the orifice into the milk 

 cistern. 



Symptoms. Mastitis occurs almost wholly in cows in full 

 milk, and chiefly very soon after calving. It is at this time 

 that the udder is most active, and consequently offers the great- 

 est vulnerability to infection, and it is at this period that the 

 udder is most exposed to virulent infections of various kinds. 

 The maximum distension of the udder subjects the secretory 

 tissues to a compression, which, if not promptly relieved by milk- 

 ing, lowers the powers of resistance in the parenchyma of the 

 gland. At the same time, the engorgement causes the udder to 

 oroject farther, more directly and rigidly from the body walls, 



