232 GENERAL THERAPEUTICS FOR VETERINARIANS 



4. Desiccation. Just as with high degrees of heat, the viru- 

 lence of some contagions is reduced by drying (withdrawal of 

 water). This method of mitigation has been of practical use in 

 Pasteur's rabies vaccination, also in black leg vaccination (Kitt) 

 and in part in cow pox inoculation (vaccination). In the Pasteur 

 process small pieces of the spinal cord of a rabbit affected with 

 rabies are suspended in bottles and dried; to hasten desiccation 

 the bottom of the bottle is covered with small pieces of caustic 

 potash and at the same time the bottles are held constantly 

 at a temperature of 20° C. By this method the virulence of the 

 rabies virus is weakened so that after 1 to 2 days' drying 7 days 

 are required for it to produce its effects; after 3 to 5 days' drying, 

 8 days; after 6 to 9 days', 15 days, etc. As the weakest material 

 is first injected subcutaneously and stronger material at each 

 successive injection, the vaccinated animals (and man) gradu- 

 ally acquire an immunity. 



5. The influence of disinfectants. The addition of anti- 

 septics to cultures of bacteria also reduces their virulence. For 

 this purpose carbolic acid, potassium chromate, iodine trichloride, 

 oxygen and other disinfectants have been used in anthrax, tetanus, 

 pox, diphtheria, etc. Sunlight and certain physical factors (high 

 atmospheric pressure) also appear to have an attenuating effect. 



6. The progressive inoculation of material of increasing 

 virulence. By inoculating first weakened, then more virulent, and 

 finally infectious material which has not been attenuated, the 

 organism gradually becomes accustomed to the contagion. This 

 process is employed in Pasteur's rabies and anthrax vaccination, 

 in Lorenz's swine erysipelas vaccination (first serum, then culture 

 inoculation), in Koch's vaccination for rinderpest (first bile, then 

 virulent blood), and in other infections. In vaccination for swine 

 erysipelas and rinderpest the weakened and the strong vaccine 

 have been inoculated at the same time (sunultaneous inocu- 

 lation). 



7. Long-continued cultivation of the infectious material. As 

 was first shown by Pasteur, the virulence of a pathogenic organ- 



