702 INFECTION OF THE UDDER. 



of disturbances which readily assume an acute inflammatory character. 

 It is, therefore, very natural that most diseases of this kind occur 

 after parturition. 



The anatomical formation also favours acute inflammation. The 

 milk forms an excellent cultivating medium for bacteria, to which 

 the teat ducts offer an easy point of entrance. Finally, the position 

 of the udder is exceedingly favourable to the entrance of infective 

 material ; and as injuries to the skin of the udder, and especially 

 to the teats, are frequent in animals, they easily form the point of 

 origin of infective inflammation. 



While formerly the causes of mammitis were divided into 

 mechanical, chemical, thermal and specific, to-day the cause most 

 widely accepted is infection with pathogenic organisms. No doubt 

 a limited mammitis often results in cattle from horn thrusts, fork 

 stabs, kicks, blows from the calf and similar injuries. The effects 

 of chemical or thermal irritants are less obvious, though the milk 

 may undergo changes within the udder. Chills, by disturbing 

 vasomotor control, may weaken the defences of the gland tissues 

 and promote bacterial invasion. After Franck had directed 

 attention to infection in mastitis, others described different bacteria 

 as the cause of inflammatory processes in the udder ; but later 

 investigation has shown that while numerous and varied bacteria 

 may be found in the milk or interstitial exudates in cases of mastitis, 

 only a few of these have been proved to be specific. 



Infection may occur by three paths. 



(1) The skin, which, as already remarked, often suffers slight 

 injuries, sufficient, however, to form the starting-point of infection. 

 We see, then, why cows are more frequently affected with disease 

 of this character than mares, the reason being that their teats are 

 more often injured and simultaneously infected during milking. 

 Disease once produced spreads, especially in the course of the 

 superficial lymph vessels of the udder, and therefore first affects 

 the skin and subcutaneous tissue. This method of spread 

 (lymphogenous mastitis, Kitt) is, however, less frequent than the 

 next in order, as Johne has shown. 



(2) Infection through the teat duct. In many cases pathogenic 

 bacteria pass through the duct into the galactophorous sinus, and 

 finally into the smallest divisions of the affected portion of the gland, 

 producing, according to their degree of virulence, a more or less 

 violent inflammation of the parenchyma of the udder (galactophorous 

 mastitis, Kitt). At the first glance it appears astonishing that- 

 inflammatory processes are not more frequently produced in this 



