66 INFECTION AND RESISTANCE 



rabies. Rabbits are inoculated with virus fixe, and their spinal 

 cords dried for varying periods in bottles containing KOH at a tem- 

 perature of about 25 C. The virus grows progressively weaker 

 with each day of drying. Greater details concerning this method are 

 given in another place (see page 489). 



(6) Attenuation by the use of chemicals. Chamberland and 

 Roux 19 succeeded in attenuating anthrax by growing it in the 

 presence of various antiseptics. They used carbolic acid 1 to 600, 

 bichromate of potassium 1 to 1,500 and sulphuric acid 1 to 200, 

 and found that, after a short time of cultivation under such condi- 

 tions, the bacilli lost their ability to form spores and became avirulent 

 for sheep. Behring 20 and others have applied this method to the 

 attenuation of diphtheria toxin; Behring adds terchlorid of iodin, 

 Roux potassium iodid iodin solutions. The principle, of course, 

 is not exactly the same in the last cases, since here the attenuation 

 is not of the bacteria themselves, but rather of the toxin. 



(7) Attenuation by cultivation under pressure. This method 

 is difficult to apply, and has no striking advantages over other pro- 

 cedures. It was employed by Chauveau 21 for the attenuation of 

 anthrax. He succeeded in accomplishing this by cultivation of 

 anthrax bacilli at 28-39 C. at a pressure of 8 atmospheres. 



II. ACTIVE IMMUNIZATION WITH FULLY VIEULENT CULTURES IN 



SUBLETHAL AMOUNTS 



The original methods of Pasteur carried out with chicken cholera 

 and anthrax were aimed particularly at diminution of virulence, 

 since these organisms, as isolated from the diseased animal, are so 

 extremely infectious that it would be very difficult (in the case of 

 many animals, impossible) to inoculate with the unattenuated 

 germs without producing fatal disease. However, in the case of 

 many other infections it has been found feasible to inoculate normal 

 animals with the fully virulent germs in such small quantities that 

 the body can successfully overcome them, and, in doing so, acquire 

 specific resistance. It is obvious that this method is more easily 

 carried out with the organisms which Bail terms "half parasites" 

 than with organisms as highly infectious as anthrax. Ferran 22 

 applied this method both to animals and to human beings with broth 

 cultures of cholera spirilla. Hogyes 23 has introduced a similar 

 procedure for immunization against rabies by injecting dilutions of 



19 Chamberland and Roux. Compt. rend de I'acad. des sc., 96, 1882. 



20 Behring and Wernicke. Zeitschr. f. Hyg., 12, 1892. 



21 Chauveau. Compt. rend, de I'acad. des sc., Vol. 98, 1884. 



22 Ferran, Compt. rend, de I'acad. des sc., 1885. 



23 Hogyes. "Lyssa Nothnagels Handbuch, etc.," Vienna, 1897. 



