CHAPTER XXIII. 

 ARTIFICIAL IMMUNIZATION. 



ACTIVE IMMUNITY — PROPHYLACTIC INOCULATION. 



The principle of active immunity against certain contagious diseases, such 

 as Jenner's vaccination and Pasteur's antirabid inoculation, has long been 

 known to medicine. The attempt, however, to produce a state of increased 

 resistance to a more rapidly acting poison through the same procedure was 

 not made until many years after Pasteur's brilliant discovery. This was 

 done first by Henry Sewall with the venom of Sistrurus catenatus (or Cro- 

 talophorus tergeminus) upon pigeons. In 1886 to 1887 this investigator * 

 conducted a series of experiments in which he successfully produced active 

 immunity against this venom in pigeons by means of repeated injections of 

 non-fatal doses at varying intervals of time between each injection. Pigeons 

 are known to be highly sensitive to the fatal effect of crotalus venom. Sewall 

 carefully estimated the minimal fatal dose of the venom and then after a period 

 of many months of "prophylactic injections" several pigeons, which with- 

 stood the immunization, were tested for their resistance to the action of the 

 venom. It was found that some pigeons showed no symptoms when injected 

 with even 10 minimal lethal doses, whereas the control birds succumbed in 

 several hours with the usual paralytic symptoms. Sewall also observed that 

 the immunity gradually declined in the absence of fresh injections of the 

 venom, and that even 5 months after the last injection the birds may still 

 show quite marked resistance. Sewall's work antedates by a couple of years 

 the renowned discovery of Behring and Kitasato of the diphtheria antitoxin. 



Kaufmann 2 also recognized that immunity to viperine venom could be 

 secured by repeated sublethal injections. 



The importance of the subject of immunity and immunization to venom 

 now became evident, and the work of Phisalix and Bertrand directly bridges 

 the gap between active immunity and passive immunity in snake venom. 

 In 1894 these investigators 3 found that it was possible to immunize 

 guinea-pigs to the action of serpent's venom. The reduction of the toxicity 

 of venom by heat ^ was interpreted by them as due to the conversion of 

 the poisonous principle of venom into the vaccinating principle. Only a 

 portion of the venom undergoes this change, however, enough remaining 



1 Hemy Sewall. Experiments on the preventive inoculation of rattlesnake venom. Jour, of Physiol., 



1887, VIII, 203. 



2 Kaufmann. Les Viperes de France, morsures, traitements. Paris, 1893. 



3 Phisalix and Bertrand. Vaccination et accoutumance du cobaye contre le venin de vipere. Atti 



d. Cong. Med. internaz., Roma, 1894, II, Pat. gen. ed Anat. parol., 200. Attenuation du venin 

 de vipere par la chaleur et vaccination du cobaye contre le venin. Compt. rend. d. l'Acad. d. 

 Sci. Paris, 1894, CXVIII, 285. 



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