256 



VENOMOUS ANIMALS 



The results were as follows : — 



Control guinea-pig died in 45 minutes. 

 Brain-injection guinea-pig died in 19 hours. 

 Blood-injection guinea-pig died in 3 hours 50 minutes. 

 Adrenals-injection guinea-pig died in 2 hours 35 minutes. 

 Spleen-injection guinea-pig died in 2 hours 10 minutes. 

 Liver-injection guinea-pig died in i hour 30 minutes. 

 Kidney-injection guinea-pig died in i hour 55 minutes. 

 Muscles-injection guinea-pig died in i hour 30 minutes. 



Next they tried two M.L.D., with the following results: — 

 Brain-injection guinea-pig survived. 

 Blood-injection guinea-pig died in 28 hours. 

 Liver-injection guinea-pig died in 19 hours. 



From these experiments they conclude that snake-venom con- 

 tains a neurotoxic principle, which is the chief poison, and which 

 unites in multiple minimal doses with the nerve cells, but that, even 

 if this chief toxic principle be removed, there is still left sufficient 

 haemolysin to cause death. 



This neurotoxic substance has been shown by Rogers in the 

 cobra and the Hydrophidae to attack the respiratory centre in the 

 medulla, the respirations becoming both fewer in number and less 

 in amplitude minute by minute, until they cease if sufficiently large 

 doses are administered, but when smaller doses are given there is at 

 first a temporary stimulation. 



Further, he shows that the neurotoxic substance can paralyze 

 the end-plates of the phrenic nerves in the diaphragm shortly after 

 the failure of the respiratory centre in the medulla. 



The blood-pressure does not appear to be affected by the poison, 

 and, in fact, the circulation can be kept going for a long time after 

 cessation of breathing if artificial respiration is resorted to — a fact 

 first shown by Brunton and Fayrer. 



On the other hand, with regard to viperine snakes — -e.g., Vipera 

 russellii, Bitis arietans, Crotalus horridus, and Lachesis anamallensis 

 ■ — Rogers concluded that the neurotoxin acted upon the vasomotor 

 centre in the medulla — a point which was noted by Weir Mitchell 

 and Reichert as a cause of the variation of the blood-pressure in 

 Crotalus poisoning. 



There are thus several neurotoxic elements in snake-venom, of 

 which two great groups can at present be provisionally described: 



(1) Colubrine neurotoxic element, acting upon the^ — -(i) Respira- 

 tory centre in the medulla; (2) the end-plates of the phrenic nerve. 



(2) Viperine neurotoxic element, acting upon the vasomotor 

 centre in the medulla. 



Kilvington has studied the effects of the venom of Hoplocephalus 

 curtus Giintber {Brachyaspis curta Schleg.) on nerve cells, and 

 found that the nerve cells of the central part of the cervical enlarge- 

 ment showed a breaking-up of the Nissl granules into a fine dust- 

 like deposit. The nucleus may become indistinct, but it remains 



