464 WSEASES OF CATTLE. 



This vaccine, which is in the form of a brownish, dry powder, is 

 mixed with definite quantities of sterile water, filtered, and by means 

 of a hypodermic syringe the filtrate injected under the skin in front 

 of the shoulder of the animal. The inoculation is usually followed by 

 insigiiificant symptoms. In a few cases there is a slight rise of tem- 

 perature, and by close observation a minute swelling may be nottd at 

 the point of inoculation. The immunity conferred in this way may 

 last for 18 months, but animals vaccinated before they are 6 months 

 old and those in badly infected districts should be revaccinated before 

 the following blackleg season. 



The effect of the vaccine prepared by this bureau in preventing 

 outbreaks of the disease and in immediately abating outbreaks 

 already in progress was highly satisfactory, and it is not to be doubted 

 that thousands of young cattle were saved to the stock owners during 

 the 25 years in which the vaccine was distributed.^ More than 

 47,000,000 doses were sent out during this period, and from reports 

 received it is safe to conclude that more than 40,000,000 were actually 

 injected, wherdby the percentage of loss from blackleg has been re- 

 duced from 10 per cent, which annually occurred before using, to less 

 than one-half of 1 per cent per annum. With these figures before us it 

 is plain that the general introduction of preventive vaccination must 

 be of material benefit to the cattle raisers in the infected districts. 

 Moreover, there is every reason to believe that with the continued 

 use of blackleg vaccine in all districts where the disease is known to 

 occur, and an earnest effort on the part of the stock owners to prevent 

 the reinfection of their pastures by following the directions given, 

 blackleg may be kept in check and gradually eradicated. 



Immunization against blackleg is now frequently accomplished by 

 the use of the so-called blackleg aggressin and blackleg filtrates. 



NECROTIC STOMATITIS (CALF DIPHTHERIA). 



[PI. XLIII.] 



Necrotic stomatitis is an acute, specific, highly contagious inflam- 

 mation of the mouth occurring in young cattle, and characterized 

 locally by the formation of ulcers and caseo-necrotic patches and by 

 constitutional symptoms, chiefly toxic. 



This disease has also been termed calf diphtheria, gangrenous 

 stomatitis, ulcerative stomatitis, malignant stomatitis, tubercular 

 stomatitis, and diphtheritic patches of the oral mucous membrane. 



History. — During the last few years fai-mers and cattlemen in this 

 country, especially in Colorado, Texas, and South Dakota, have 

 increasingly noted the occurrence of enzootics of " sore mouth " 

 among the young animals of their herds. Instead of healing, like the 

 usual forms, of themselves, these cases, if untreated, die. Careful 

 study of some of them has resulted in their identification with cases 



» The distribution of Government blackleg vaccine was discontinued July 1, 1922. 



