14 MASTITIS OF THE COW 



in old milch cows, or a more severe affection, as a chill or 

 fever,^ causes the same alteration, and dilatation of the milk 

 canal takes place and predisposes to infection. 



Infection may be induced by the introduction of in- 

 struments, as a milk tube in the teat canal, or spontaneously 

 with foreign bodies, as a straw which may be forced into 

 the teat canal when the cow lies down. 



Predisposing Factors of a Biological Nature. — When 

 a very virulent rapidly growing bacillus gains access to 

 the mouth of the teat canal it can always find spaces in 

 that passage containing moisture from the physiological 

 capillaries in which it can grow. Through its own virulence 

 it can withstand the leucocytes (negative chemotaxis) [ag- 

 gressins], and infect the milk. This explains the distinctly 

 contagious character of many cases of mastitis. 



Prophylactic Measures Against Infection Through the 

 Teat Canal. — Avoid arrest of the milk secretion by well- 

 regulated milking hours and punctuality in milking. Use 

 the milk tube cautiously. Keep the teats clean and dry. 

 In cases of contagious mastitis isolate the diseased indi- 

 vidual, milk it last and disinfect the morbid milk in order 

 to avoid the possibility of spreading the infectious material 

 in the cow stable. 



UDDER WOUNDS AS PORTS OF ENTRANCE 



Udder wounds may already be infected from the be- 

 ginning, that is, the infectious material is injected at the 

 same time that the wound is made. Such is often the case 

 in stab wounds. In other cases a wound may be sterile 

 at first and become infected later. 



In fresh wounds the exterior of the wound itself and 

 also the milk through the ruptured tubules may become 



^ Both appear to be followed by paresis of the involuntary 

 muscles which among other things produces diminished peristaltic 

 action. 



