54 Blackleg. 



cauped no loss, and no case o^ blackleg appeared among the vaccinated animais 

 during the following year. 



In the United States this method has been much in use since 1897, with the 

 modification however that Norgaard heats the dried ground muscle intended for vacci- 

 nation only to 93-94°C. The Bureau of Animal Industry sends out li/4 millions of 

 doses of vaccine every year, and tlie results of the vaccinations have been favorable. 

 Thus, in the years 1907-08, out of 690,828 vaccinated animals 227 died within 48 

 hours after vaccination, 507 from 2 to 7 days after, and 2,734 later within a 

 year (total loss 0.50%). 



In India, Holmes obtained the best results from one injection of a mixture 

 of the first and second Lyons vaccine, which by means of a particularly con- 

 structed syringe was placed under the skin in the shape of a pill. 



III. Immunization with serum and attenuated cultures. 



Kitt (1893-1899) obtained from sheep wliicli had been treated 

 repeatedly with intravenous and later with subcutaneous in- 

 jections of muscle juice from blackleg tumors, a blood serum 

 which in 5 to 10 cc. doses protected sheep against an injection 

 of the virus made 3 to 8 days later, and 15 cc. injected into a 

 goat cured the already developing disease. According to later 

 investigations (1899), goats, cattle and horses also produce 

 similar active blood sera, and the last named animal partic- 

 ularly seems to be suitable for the purpose. 



These results were later confirmed by Arloing, and still 

 later by Leclainche & Vallee; besides, the latter authors have 

 ascertained that blood serum and virus mixed together, or eacli 

 for itself when injected at the same time, do not immunize, 

 but that the successive application of blood serum and virus 

 affords a mode of immunizing, which may be used for practical 

 purposes. 



The method which has so far oeen tested only in France is as 

 follows : For vaccination two different vaccines are used. The one 

 is blood serum from horses, which, through repeated intravenous injec- 

 tions with bouillon cultures of the blackleg bacillus containing toxins, 

 have been highly immunized ; the other is a bouillon culture of the 

 same bacillus attenuated by being heated to 70° C. for 3 hours. First 

 the animals are injected with 10 to 20 cc. of blood serum, according to 

 their weight, in the region of the shoulder, and 5 to 6 days later a 

 second injection is given subcutaneously with 0.5 to 1.0 cc. of attenu- 

 ated pure culture at the same place or in the neck, ear or tail. This 

 form of protective vaccination may also be applied without hesitation 

 in already infected herds. 



Leclainche & Vallee vaccinated in the year 1902, 447 head of cattle without 

 any direct loss, but subsequently one animal died from blackleg; later statistics 

 indicate 8 deaths among 7,987 vaccinated animals (0.1002%). 



According to Leclainche & Vallee some of the animals on blackleg pastures 

 harbor the virus in the intestinal canal (latent infection), but they are protected 

 against its pathogenic action by the intestinal juices and phagocytosis; if, however, 

 such animals are inoculated with live, even attenuated, virus, the body thus attacked 

 from two sides, can no longer combat the infection. Through the preceding vaccina- 

 tion with serum, the resistance of the animal is increased to such a degree through 

 the production of passive immunity as to make it efficient even against the double 

 danger. This conception can hardly be recognized as correct in its present form, 

 because after vaccination of already diseased herds with live virus direct losses from 

 the vaccination are seldom observed. To the occurrence of such losses other factors 

 are contributory, particularly the relative susceptibility of the animal in comparison 

 with the degree of virulence of the vaccine. 



