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? 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? 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 
ee eS 
1 Henry Sewall. Experiments on the preventive inoculation of rattlesnake venom. Jour. of Physiol., 
1887, VIII, 203. 
2Kaufmann. Les Vipéres de France, morsures, traitements. Paris, 1893. 
8 Phisalixeand Bertrand. Vaccination et accoutumance du cobaye contre le venin de vipére. Atti 
d. Cong. Med. internaz., Roma, 1894, II, Pat. gen. ed Anat. patol., 200. Atténuation du venin 
de vipére par la chaleur et vaccination du cobaye contre le venin. Compt. rend. d. V Acad. d. 
Sci. Paris, 1894, CXVIII, 285. 
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