226 VENOMOUS SNAKES AND THE PHENOMENA OF THEIR VENOMS 



The principles of immunization Calmette resorted to were: 

 (i) Accustoming the animal to frequently repeated, gradually increased 

 doses of diluted venom. 



(2) The administration of a fatal dose of venom, followed by immediate 

 curative therapeutic treatment with chloride of calcium or gold. 



(3) The administration of repeated increasing doses of venom mixed 

 with the chloride of calcium or gold. 



Of these three methods he preferred the first. The serums obtained from 

 the immunized animals showed preventive as well as curative effects in ani- 

 mal experiments. 



Somewhat later Calmette ^ added to the above facts that the antitoxic 

 property of his antivenin was equally effective in counteracting the action of 

 all kinds of snake venoms, namely, those of vipers, Notechis scutatus and 

 Pseudechis porphyriacus, as well as that of cobra, with which it was prepared. 

 This statement, and also another, that the immunity can be developed by 

 repeated injections of weak solutions of alkahne hypochlorites without the 

 venom, have since undergone a complete modification through more careful 

 and extended investigations by later workers on this subject, and to-day the 

 question of specificity of antivenin may be considered as settled against this 

 assertion. To this point I shall return at length. 



As his study progressed Calmette ^ at last found another method of immuni- 

 zation, namely, by injecting animals with gradually increasing doses of venom 

 modified by heat. He pointed out that the temperature of 75° C. inactivates 

 all the local irritant and oedema-producing principles without affecting the 

 activity and the immunizing quality of the venom. After 48 hours the ani- 

 mals readily endure a fatal dose of venom and at the end of a month have 

 quite a high immunity. At this time Calmette was still uncertain of the 

 therapeutic value of the antivenin for the treatment of snake bite. 



He ^ next prepared the antivenin by immunizing two asses to venom (cobra) 

 previously heated. The first received 0.0022 gm. within a period of 97 days 

 and another 0.0016 gm. within 76 days. The serum of the first was of such 

 antitoxic value that 0.5 c.c. neutralized o.ooi gm. of the venom; 4 c.c. of the 

 serum injected 4 hours before the venom protected against 2 minimal lethal 

 doses. If one inoculated a rabbit with enough venom to kill a control rabbit 

 in 3 hours, and an hour subsequently administered 4 to 5 c.c. of the scrum, 

 the animal recovered. The later the therapeutic serum is administered, 

 however, the less certain is recovery to take place, so that Calmette in his 

 experiments placed i^ hours as the limit of certain cure. He observed that 

 the local action of the highly irritative venoms of Crotalus, Lachesis cerastes, 

 and L. trigonocephalus is always present when these venoms are injected into 

 the immunized animals. 



1 Calmette. Proprietes du serum des animaux immunises centre le venin des serpents, therapeutique 



de I'envenimation. Compt. rend. d. I'Acad. d. Sci., Paris, 1894, CXVIII, 720; Atti XI. Cong. 

 Med. internaz., Roma, 1894, II, Patol. gen. ed Anat. patol., 109. 



2 Calmette. Contribution a I'etude du venin des serpents. Ann. I'lnst. Pasteur, 1894, VIII, 275. 

 ^ Calmette. Ibid., 1895, IX, 225. 



