186 PUBLIC HEALTH BACTERIOLOGY 



but at times was severe and even fatal. In contagious 

 pleuro-pneumonia of cattle, subcutaneous injection of the 

 lymph of a newly killed animal, into the tail, has proved 

 protective. The animal sometimes loses its tail in part, 

 the brunt of the infection apparently remaining localized. 



(6). With attenuated virus. This is accomplished in 

 one or more of the following ways : 



By cultivation of the organism in oxygen or a current of 

 air, as first discovered by Pasteur in the case of the bacilli 

 of chicken cholera. The attenuated bacilli, on injection, 

 produced a non-fatal disease, which immunized the fowl, 

 especially on repetition. 



By cultivation of the bacteria at high temperatures, 

 e.g., anthrax bacilli at 42 to 43 C. 



By passage through a less susceptible species. This is 

 the presently accepted explanation of vaccination for 

 small-pox. Used by Pasteur for swine erysipelas, the 

 bacillus of which is lessened in virulence by repeated 

 passage through rabbits, but increased by passage through 

 pigeons. Two inoculations were given, the first of the 

 attenuated bacilli from rabbits, the second of the exalted 

 bacilli from pigeons. 



By drying the virus, as in hydrophobia, where Pasteur 

 found that the virus was exalted in virulence by successive 

 subdural passage through rabbits, but diminished by 

 passage through apes. He tried the immunization of dogs 

 by the use of the diminished and increased viruses, but 

 the results were too variable, so he tried drying the spinal 

 cord of a rabbit dead of the disease. A cord thus dried at 

 22 C. over KOH (to absorb CO 2 ) for i to 4 days, still 

 causes rabies in 7 days (the incubation period shortened 

 from 14 days by the exaltation of the virus) ; but if kept 

 longer, the incubation period is prolonged, until one kept 

 12 to 14 days has become inactive. The treatment 

 consists in beginning with injection of an emulsion of this 

 cord, and daily repeating with an emulsion of a less dried 

 cord until within 15 days in mild cases and 21 days in 

 severe, the strength arrived at is a 3-day-dried cord. 

 Complete immunity thus takes 3 to 4 weeks, and so in 

 cases coming under treatment at a late period, the 

 method is condensed. Hoegyes uses fresh cord emulsified 



