CHAPTER IV 



INFECTIOUS MASTITIS IN GENERAL 



Ports of Infection 



The causes of infection may enter the udder: {a) 

 through openings in the udder, and ( b ) through the blood- 

 stream. 



The openings which may serve as ports of infection to 

 the udder are of two diiFerent types: (1) natural: the teat 

 canals, and (2) morbid: wounds. 



THE TEAT CANAL AS A PORT OF INFECTION 



Infectious material enters through the teat canal, so 

 that first the milk and indirectly through it the tissue 

 become infected. 



The milk is a nutritious fluid and contains water, salts, 

 albumin, carbohydrates, and fats. It is an excellent source 

 of nourishment for bacteria and therefore difficult to pre- 

 serve, especially in summer, since it easily undergoes acid 

 fermentation in vessels. 



The udder keeps the milk warm, like a thermostat, and 

 offers very favorable conditions for bacterial development. 



Under normal conditions, however, the milk in the 

 udder is practically sterile. The reasons for this are of 

 two types: (a) physical nature, and (b) biological nature. 



Physiological causes of sterility of milk in the udder. 

 The teat canal is closed between milkings by bundles of 

 smooth muscle tissue imbedded in the walls which maintain 

 a definite moderate tension. Thus under physiological 

 conditions the external opening of the teat canal is small, 

 usually rendering infection more difficult. 



Furthermore, the teat canal is directed downward, or to 

 the side when the cow is lying, but never upward, as the 



12 



