TUBERCULIN AND MALLEIN 181 



greater difficulty through animal parchment : they resist heating 

 at ioo° C. and are only completely destroyed at 115-120°. 



From the chemical point of view both consist of proto- 

 and deutero-albumoses : the alburriins they contain are not 

 toxic. S. Faust has extracted from cobra venom an "ophio- 

 toxin" which contains neither nitrogen nor sulphur nor 

 phosphorus. 



By using dried venom, which can be accurately dosed by 

 redissolving in a known volume, it has been possible, as with the 

 vegetable toxins, to determine the minimal lethal dose per 

 kilogram in different species of animal. As with tetanus toxin 

 the size of the animal bears no relation to its sensitiveness. 

 With one gram of dry cobra-venom it is possible to kill 1,250 

 kilos, weight of dog, 2,000 k. of rabbit, 2,500 k. of guinea-pig, 

 1,430 k. of rat, 8,333 k. of mouse, 20,000 k. of horse, and 

 10,000 of man, i.e., 165 adults of average weight. The horse 

 is thus the most sensitive of all these animals. 



The toxicity of the venom is very variable : it is more 

 active (and doubtless less abundant) after the casting of the 

 skin and after a prolonged fast. 



Physiological Action of Snake-venoms. — The 

 physiological action of snake-venoms is complex. They act 

 on the cells of the organs, on the liver, the kidney, and the 

 spleen : on the endothelial cells which line the interior of the 

 blood vessels (especially the rattlesnake poisons) : on the nervous 

 system (according to Rogers the venoms of the Viperidae 

 paralyse the vasomotor centres, those of the Colubridae the 

 respiratory centres) : on the blood, one of the oldest known 

 effects and one much studied recently because the solution of 

 the red corpuscles or haemolysis is a phenomenon very obvious 

 and easy to study in vitro. The condition of the blood at 

 autopsy varies according to the dose of the poison and the 

 time; this is why the same poison is called coagulant or 

 anticoagulant by different workers. 



Snake-venoms have the properties of digestive ferments. 

 They can dissolve coagulated blood and can destroy the cells 

 of the vessel coats and even of the muscles. Cobra-venom 



