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of the duct. The use of a filthy or rough dilator or milk 

 tube may irritate the membrane. The most common 

 cause, of infection, according to my observations, is the 

 employment of filthy finger nails or a dirty knife to re- 

 move a clot or a temporary obstruction in the duct. The 

 thickening of the lining membrane is usually near the 

 lower end of the duct, but in one instance I found the 

 duct obstructed in the entire length in all four tests; and, 

 according to the owner, the cow was not carefully or 

 properly "dried up." 



The duct in the teat may, also, be obstructed by a 

 growth in the substance of the teat, which presses on the 

 duct and obstructs the flow of milk. The growth may be 

 in or on the lining membrane of duct and anywhere 

 along its course, but most frequently at its lower end. 

 In some cases a false membrane develops across the milk 

 sinus or reservoir preventing the flow of milk into the 

 teat; this can be determined by using the milk tube or 

 probe or small dilator. 



In extremely rare instances lime-like deposits may take 

 place in the milk ducts and sinuses, and appear in the 

 duct of the teat as sand-like grains or particles obstruct- 

 ing the flow of milk. 



The most common causes of obstruction of the flow of 

 milk in the teat are clots of milk (casein) resulting from 

 infection of the milk by germs getting into the udder 

 through the duct in the teat; retention of milk in the 

 udder for a long time; and catxirrhal and other forms 

 of inflammation in the udder. Milk is a good food for 

 o-erms, and various kind' of bacteria will grow in it, 

 many of which will precipitate the casein, thus forming 

 clots in the sinus of the udder. 



Treatment of obstructions will vary with the condi- 

 tions presented. Narrowing of the duct may sometimes 

 be relieved by using dilators ( flgs. 1,2) ; it may be neces- 



