374 Hydrophobia, Lyssa, or Rabies 



powerful germicides to the wounds made by the dog's teeth, and 

 Lambert who worked upon this matter experimentally came to the 

 conclusion that though a few cases might thus be saved, the method 

 was too unreliable to be recommended. The long period of incuba- 

 tion of human rabies (from 15 to 250 days and averaging 40 days) 

 is the source of salvation for many infected persons, for it makes it 

 possible to effect immunization during that period and so inhibit 

 the development of the disease itself. 



Immunization against Rabies. — Pasteur* observed that the viru- 

 lence of the virus was less in animals that had been dead for some time 

 than in those just killed, and by experiment found that when the 

 nervous system of an infected rabbit was dried in a sterile atmos- 

 phere its virulence attenuated in proportion to the length of time 

 it was kept. A method of attenuating the virulence was thus sug- 

 gested to Pasteur, and the idea of using attenuated virus as a pro- 

 tective vaccine soon followed. After careful experimentation he 

 found that by inoculating a dog with much attenuated, then with 

 less attenuated, then with moderately strong virus, it developed 

 an immunity that enabled it to resist infection with an amount of 

 virulent material that would certainly kill an unprotected dog. 



It is remarkable that this method, based upon limited accurate 

 biologic knowledge, and upon experience with very few micro-organ- 

 isms, should find absolute confirmation as our knowledge of im- 

 munity, toxins^ and antitoxins progressed. Pasteur introduced the 

 unknown poison-producers, attenuated by drying and capable of 

 generating only a little poison, accustomed the animal first to 

 them and then to stronger and stronger ones until immunity was 

 established. 



For the treatment of infected cases exactly the same method is 

 followed as for the production of immunity. Indeed, the treatment 

 of a patient bitten by a rabid animal is simply the production of 

 immunity during the prolonged incubation period of the affection, 

 so that the disease may not develop. The patient, to be successfully 

 treated, must come under observation early. 



The Attenuation Method. — To protect human beings from the 

 development of hydrophobia after they have been bitten by rabid 

 animals, it is necessary to use material of standard or known viru- 

 lence. This can be prepared, according to the directions of Hogyes,t 

 by the passage of virus from a rabid animal through from 21 to 30 

 rabbits. 



For this purpose some of the hippocampal tissue of the dog is made into an 

 emulsion with sterile salt solution and injected subcutaneously into a rabbit. 

 As soon as this animal dies, its spinal cord is removed, a similar emulsion made 

 with a fragment of it, and a second rabbit inoculated, and so on through the 

 series until a standard virulence is attained and the virus is said to be "fixed.'. 



* "Compt-rendu del' Acad, de Sciences de Paris, "xcn, i259;xcv, 1187, xcvra> 

 457, 1229; CI, 76s; cii, 459, 835; era, 777. 



t See Kraus and Levaditi, "Handbuch der Immunitatsforschung," i. 



