VACCINATION. IMMUNIZATION. INOCULATION 249 



aJent coli serum (Jensen) is effective, but the protective vaccination of cows 

 in advanced pregnancy has, on the contrary, proven to be without value. 



Fowl Cholera. — 1. Protective Vaccination with Attenuated Cud- 

 TUBES According to Pasteur. — In 1880, Pasteur recommended the vaccina- 

 tion of healthy individuals with cholera bacilli attenuated by cultivation as 

 the most effective method of combating fowl cholera. He found that vacci- 

 nation with a weakened (mitigated) vaccine produced only a local swelling 

 at the point of inoculation and that the muscle tissue beneath underwent 

 necrosis without suppuration. The vaccinated bird was sick, indeed, but did 

 not die and became immune to the disease. Some chickens, however, required 

 2 to 3 vaccinations with mitigated vaccine before they acquired an immunity. 

 Pasteur therefore introduced a double vaccination, first injecting a very weak 

 vaccine (premier vaccine) and then a stronger one (deuxieme vaccine). The 

 bacilli were attenuated by keeping them for 3 to 10 months under conditions 

 which permitted the entrance of air, whereby, according to Pasteur's theory* 

 their virulence was reduced by the oxygen of the air. Protective vaccinations 

 were made according to this method by Cagny, Hess, and Kitt, and the results 

 were very unfavorable (spread of the disease, fatal cases). 



2. Serum Vaccination has been of doubtful value in Prussia, but in 

 Denmark very favorable results have been obtained. 



Contagious Pneumonia of Horses. — The first senma vaccinations were 

 made by Hell in 1892. The vaccinations made the same year in the Prussian 

 army to test the new process were, however, without effect, since the disease 

 occurred with the same intensity in the vaccinated horses as in those which 

 had not been vaccinated, while many horses which were not vaccinated did 

 not take the disease (P. Mil. V. B., 1892). The reports concerning the vacci- 

 nations made in the army with blood-serum in 1893 are very contradictory 

 (P. Mil. V. B., 1893). In 1894, vaccinations were made in four regiments. 

 The results did not speak favorably for the vaccination; it neither shortened 

 the course of the disease nor reduced the virulence. The isolated favorable 

 results were only apparent and are to be explained by the benign character 

 of the infection (P. Mil. V. B., 1894). In 1895 the serum vaccinations were 

 also without effect, although every horse received 200 grams of serum in four 

 days; 10 weeks after the vaccinations 10 horses in one squadron became ill 

 with contagious pneumonia, some being very severely affected (P. Mil. V. B., 

 1895). On account of these results the vaccinations were discontinued in the 

 army in 1896. In 1898 Topper made a report of his experiences with blood- 

 serum vaccinations and stated that the horses became immune 6 to 8 weeks 

 after the injection of the serum. He also stated that the disease usually pre- 

 vailed in the stable 4 to 6 weeks before the vaccinations were begun and that 

 after the vaccinations it was always immediately checked. Not less than 150 



