466 DISEASES OF CATTLE. 



lips, and pharynx. In the majority of cases the primary infection 

 seems to occur in the tongue. (PI. XLIII.) 



Infection takes place by inoculation. Some abrasion or break in 

 the continuity of the mucous membrane of the mouth occurs. Very 

 likely the origin may be connected with the eruption of the firet teeth 

 after birth, or, in animals somewhat older, the entrance of a sharp- 

 pointed particle of feed. Gaining an entrance at this point, the 

 bacilli begin to multiply. During their development they elaborate 

 a toxin, or poisonous substance, which causes the death, or necrosis, 

 of the epithelial, or superficial, layer of the mucous membrane and 

 also of the white blood cells which have sallied forth through the 

 vessel walls to the defense of the tissues against the bacillary attack. 

 This destruction of the surface epithelium seems to be the essential 

 factor in the production of the caseous patch, often called the false 

 membrane. From the connective-tissue framework below is poured 

 forth an inflammatory exudate highly albuminous or rich in fibrin- 

 forming elements. When this exudate and the necrosed cellular 

 elements come in contact, the latter furnish a fibrin ferment which 

 transforms the exduate into a fibrinous mass. This process is loiown 

 as coagulation necrosis, and the resulting fibroid mass, containing in 

 its meshes the necrosed and degenerated epithelium and" leucocytes, 

 constitutes the diphtheritic or false membrane. Did the process cease 

 at this point it would be properly called a diphtheritic inflammation, 

 but it does not. A caseating ferment is supplied by the bacilli, and 

 this, acting upon the fibroid patch, transforms it into a dry, finely 

 granular, yellowish mass of tissue detritus resembling cheese. 



Frequently this caseous inflammation results in the formation of 

 one or more ulcers with thickened, slightly reddened bordere, sur- 

 mounted by several layers of this necrosed tissue. The floor of the 

 ulcer is formed by a grayish-yellow, corroded surface, under which 

 the tissue is transformed into a dry, friable, or firm cheesy mass. In 

 the tongue this may progress to two fingers' thickness into the mus- 

 cular portion; in the cheek it may form an external opening, per- 

 mitting fluids to escape from the mouth; upon the palate it fre- 

 quently reaches and includes the bone in its destinictive course; upon 

 the gums it has produced necrosis of the tooth sockets, causing loss 

 of the teeth. In the advanced forms, caseous foci may be seen in the 

 lung and in the liver and necrotic patches observed on the mucous 

 membrane of the gastrointestinal tract. 



Sym/ptxyms. — Necrotic st(Mnatitis is both a local and a systemic 

 affection. Primarily it is local. The local lesion is the caseo-necrotic 

 patch or ulcer developed as a result of the multiplication of the 

 bacilli at the point of inoculation. The general affection is an intoxi- 

 cation, or poisoning, of the whole system produced by a soluble toxin 

 elaborated by the bacilli. 



