342 EF [•"!•: CTS OF SNAKli V1-:NU.M.S ON ])O.Mi:S'rU ANIMALS. 



( >f these the more imi)ortant are the neurotoxins, the c\'toly- 

 sins, and the fihrin ferment. These various active principles will 

 now be considered briefly. 



Neiirotoxiiis.-The neurotoxins are the most important active 

 principles of many snake venoms, especially those of the Colubrine 

 type. They have been studied in the Ancistrodon contorti-ix by 

 Flexner and Noguchi. who tested the power for anchoring- of the 

 various tissues in the body for venom. As a result of their cx- 

 l^eriments it was found that while the control guinea-pig died in 

 45 minutes after injection of two minimal lethal doses, when three 

 minimal lethal doses were emulsified with two grammes of brain 

 substance, inculcated for an hoin% centrifugalised. and the super- 

 natant fluid collected and injected into a guinea-])ig. death did 

 not occur for 19 hours, and when two minimal lethal doses were 

 used the guinea-pig survived. From these ex])eriments it was 

 concluded that snake venom contained a neurotoxic ])rinci]:)le, 

 which is the principal toxic element, and wliich unites the nuilti])le 

 minimal doses with the nerve cells; but even when this neurotoxic 

 principle is removed, there is still sufficient ha?mol\'sin left to 

 produce fatal results. Rodgers has shown tliat this neurotoxic 

 substance — in the cobra and I l\droi)inc'e — when given in small 

 doses, causes a temporary stimulation, and in large doses attacks 

 the respiratory centre, and causes the res])irations to 1)ecome 

 slower and less in amplitude minute by minute, until they eventu- 

 ally cease. He also has shown that ])aral\sis of the end ])lates of 

 the phrenic nerves in the diaphragm occurs soon after failure of 

 the respiratory centre. In the medulla neurotoxins do not seem 

 to affect the blood pressure; in fact, the circulation can be kept 

 going by artificial respiration for a long time. 



The neurotoxins in \'iperine venom, on the other hand, were 

 shown by Rodgers to act on the vaso-motor centre in the medulla, 

 causing a variation in blood pressure. It will thus be seen that 

 there are in snake venom two groups of neurotoxic elements. 



( I ) Colubrine neurotoxic elements, acting on the respira- 

 tory centre of the med;tlla. and on the end ]clates of 

 the phrenic. 



(2) Viperine neurotoxic elements, acting on the vaso-motor 

 centre. 



The agglutinins present in venom can be demonstrated /;; 

 vitro by adding to a series of test-tubes containing normal saline 

 and washed corpuscles a solution of venom A-arying in strength 

 from o.oi i)er cent, to 10 per cent., and ])lacing in the thermostat. 

 Agglutination occurs at a time varying according to the concen- 

 tration of the venom solution. These agglutinins can be destroyed 

 by heating to 80 degrees Centigrade. 



The cytolysins were shown by Flexner and Noguchi to be 

 of the nature of amboceptors which require a com])lement. which 

 is obtained in the serum of the victim. lience they are capable 

 of not only jjroducing hsemolysin, but also diminishing the bac- 

 teriolytic action of the blood. Further research on this sulcject 

 l)v Kves and Sachs showed that while in the ox. shec]) and goat 



