IMMUNITY 



271 



Excretion of the Poison. 



It is believed that the poison leaves the body principally by the 

 kidney, and to a less extent by the mucosa of the stomach, the 

 salivary and mammary glands. 



With regard to the kidney, there is some direct proof of the 

 excretion, because the urine of a dog poisoned by Enhydrina vala- 

 kadien, when injected hypodermically into a pigeon, caused death 

 in twenty- two hours. 



It is also stated that i drachm of the saliva of a dog poisoned by 

 a cobra was capable of causing death in two hours. 



With regard to excretion by the mammary glands, an infant is 

 said to have died after sucking the breast of a woman bitten by a 

 poisonous snake. 



Immunity. 



Having considered the chemical composition and physiological 

 action of the venom, the next point to be discussed is immunity to 

 its action. 



Ancient and modern peoples have equally held the belief that a person who 

 has been bitten by a poisonous snake and survived obtains some sort of 

 immunity; generally the belief has been that this immunity is capable of 

 protecting the individual against all kinds of snakes. 



Ancient fables credited the Psylli of Africa, the Marsi of Italy, and Gouni 

 of India, with immunity, on the ground that they had snake's blood in their 

 veins. 



The pig was long thought to be naturally immune; but this is a mistake, 

 for the relatively slight effect of snake-venom is due to the presence of the 

 thick layer of but slightly vascular fat which surrounds the animal's body. 

 The mong6ose [Herpestes ichneumon) is believed to be naturally immune to 

 cobra-bite. 



Acquired immunity is said to occur among natives, especially snake- 

 charmers, and Europeans who have been bitten several times by snakes. 

 The Eisowy of Western Barbary are said to have acquired such an immunity, 

 and to allow themselves to be bitten by snakes proved afterwards to be 

 poisonous by killing a fowl. The natives of Bushmanland, Namaqualand, 

 and Damaraland are said to drink the venom of snakes as a protection. 

 In Ceylon a cobra is said to have bitten a snake-charmer, and shortly after- 

 wards a bystander. The snake-charmer escaped without symptoms, the 

 bystander died. 



The first scientific attempt to produce an artificial immunity was made by 

 Sewall in 1887, when by repeated small injections he raised the resistance of 

 pigeons so high that they were able to resist ten times the minimum lethal 

 dose of the venom of a Crotalus. Kanthack also produced a partial immunity 

 to cobra- venom in 1891. Kaufmann, a little later, obtained a similar result 

 with the French viper. 



In 1892 Calmette showed that by repeated inoculation of venom 

 heated to 80° C. a certain amount of resistance was produced in 

 animals. In 1894 he made researches on the venom of the cobra, 

 and about the same time Phisalix and Bert rand investigated that 

 of the viper, and showed that animals vaccinated with venom 

 developed a true immunity, and those inoculated against the 

 cobra-venom were able to resist mortal doses of Vipera, Bungarus, 

 Cerastes, Naja haje, and Pseudechis venoms. Later they showed 



