IMMUNITY. 179 



In the human disease, bubonic plague, a nearly similar 

 procedure has been proposed by Haffkine. To protect 

 against plague, cultures of plague bacilli, previously steril- 

 ized by heat and carbolic acid are injected. (See article on 

 Bubonic Plague, Part IV.) 



Inoculation Against Rabies or Hydrophobia. The im- 

 munity produced in this case probably depends upon prin- 

 ciples similar to those underlying the examples related on 

 the preceding pages. But this question cannot be regarded 

 as settled until the organism of rabies has been isolated and 

 cultivated. Attempts to discover this organism have, as yet, 

 been futile. Pasteur discovered that rabbits are susceptible 

 to rabies when portions of the medulla oblongata of a dog 

 which has died of the disease are inserted beneath the dura 

 mater of the rabbit. Spinal cords taken from rabbits thus 

 injected are placed in a desiccating chamber. Under these 

 circumstances the unknown virus undergoes a diminution 

 in virulence. Emulsions are made from spinal cords desic- 

 cated in this manner. First the patient is injected with part 

 of an emulsion from a cord which has been desiccated a 

 longer time, and in which the virulence of the poison has 

 been much reduced. Injections are then made at intervals 

 from cords that have been subjected to desiccation for 

 shorter and shorter periods, and therefore of greater and 

 greater virulence. At the end of about the twenty-fifth day 

 the patient is supposed to be immune from rabies. The 

 period of incubation in rabies is longer than in most infec- 

 tious diseases, being usually one to two months. Al- 

 though the injections take place after he has been bitten by 

 a rabid dog, it is hoped the patient may be rendered immune 

 before the period of incubation has ended. 1 



Reports of cases managed according to this method have 

 been conflicting in the past. However, there seems no longer 



1 F. Cabot, " The Dilution Method of Immunization from Rabies," 

 Journal Experimental Medicine, Vol. IV., p. 181. 

 16 



