1904.] Study of the Action of Sea-snake Venoms. 107 



{or more probably on its nerve-ends) is masked by equally powerful 

 and direct stimulation of the cardio-inhibitory centre. In Enhydrina 

 poisoning, on the other hand, the complete absence of cardio-inhibition 

 leaves the feeble tonic action on the heart free to manifest itself, as 

 appears to be displayed in several of our tracings. We cannot other- 

 wise explain the increase in rate of the heart-beats which we have not 

 infrequently met with in our experiments. 



(4) Enhydrina venom has apparently no direct action on the vaso- 

 motor centre. Rogers found that on the injection of a Viperine 

 venom, or of the venom of the Banded Krait (Bungarus fasciatus), into 

 .an animal, a marked fall of blood pressure occurred, which was of 

 central origin. In an investigation made by one of us with Drs. Sillar 

 and Carmichael (of the Materia Medica Laboratory, Edinburgh), it 

 was found that a similar and powerful action is exerted by the venom 

 of the common Krait (B. ccerulem). The absence of any such action by 

 the venom of Enhydrina is therefore worthy of note. 



(5) The blood-pressure curve in Enhydrina poisoning is a remarkably 

 steady one, provided that moderate doses of venom are given and that 

 care is taken to avoid the injection of large volumes of fluid into the 

 blood vessels. This is due to the fact that the blood pressure is 

 exposed neither to the influence of the rival forces which act on the 

 heart so strongly in cobraism, nor to the direct vasomotor changes 

 with which we have dealt in the preceding paragraph. 



(6) The respiratory mechanism is that which is chiefly affected by 

 Enhydrina venom. If large lethal doses are employed, such as Rogers 

 appears to have confined himself to, respiration falls rapidly, and a 

 considerable rise of blood pressure, asphyxial in origin, may precede 

 death. The heart-beat then quickly slows, and blood pressure falls 

 with corresponding rapidity. 



Obviously, these are simply the phenomena of rapid asphyxiation. 

 If, however, smaller doses of venom are employed, no marked rise in 

 blood pressure occurs. The ordinary level is maintained until near the 

 occurrence of death ; the beat then slows, and the blood pressure falls. 

 Here we have an expression of gradual cardiac failure, brought about 

 by slowly progressive asphyxiation. The absence in slow Enhydrina 

 poisoning of the large asphyxial rises of pressure, wm"ch are so charac- 

 teristic of the final stages of Cobra poisoning, is readily explained Try 

 the fact that Enhydrina venom has no direct constructive action on the 

 walls of the arterioles, such as Cobra venom possesses. 



(7) As to the part of the respiratory mechanism that is affected by 

 Sea-snake venom, the rapidity with which respiration is affected, both 

 when venom is injected into a vein, and also when it is applied directly 

 to the medulla oblongata, leaves no room to doubt that the respiratory 

 centre is directly acted on by the venom. On the other hand, we have 

 shown that some degree of motor nerve-end paresis is constantly 



