130 VENOMOUS SNAKES AND THE PHENOMENA OF THEIR VENOMS 



The elaborate studies of C. J. Martin * on the physiological actions of the 

 venom of Pseudechis porphyriacus, the Australian black snake, brought out 

 many important facts concerning the action of that particular venom as well 

 as of snake venom in general. The most valuable contribution made therein 

 is the elevation of the significance of intravascular thrombosis in symptomat- 

 ology in acute venom poisoning to a definite and more prominent position 

 than that hitherto assigned to it. Martin was able to explain the cause of 

 rapid death brought about in a few minutes when a comparatively large 

 dose of the venom is injected in a small animal, by demonstrating the presence 

 of extensive intravascular thrombi in such case. Thus the sudden fall of 

 blood pressure, with violent convulsions and a vigorously beating heart, was 

 excluded from the direct actions of snake venom upon the nervous system. 

 This was later worked out more completely by Martin himself and also by 

 Lamb and others with other kinds of venoms. 



In injecting a suitable amount of the venom of Pseudechis Martin obtained 

 the type of toxication in which intravascular thrombosis is no longer a factor, 

 but typical respiratory failure takes place. He was able to show that while 

 the irritability of motor nerves and their termination plates in muscles is still 

 intact, respiration ceases independently also of the effects on circulation. 

 Here the primary paralysis of the respiratory center was conclusive. By 

 giving the venom subcutaneously Martin observed that amplitude and accel- 

 eration of the rhythmic rate of respiration increased in the beginning of 

 the poisoning. As Martin observed no influence of division of the vagus 

 on the initiatory acceleration of the respiratory function, he was led to con- 

 sider the phenomenon as directly due to the stimulus on the respiratory center 

 in the medulla. 



In regard to the sensibility of the respiratory and the circulatory systems 

 to the action of the venom, Martin states that usually a stronger concentra- 

 tion has a greater effect upon the heart, and a weaker concentration upon 

 the respiration. With a weak concentration a continued action is necessary 

 to produce marked effect upon the respiratory function. Again, vulnerability 

 of different species of animals to the venom is by no means uniform. Thus 

 dogs are more sensitive to the vascular effects than to the respiratory, while 

 with rabbits the relation is entirely reversed. 



Reflex activity of the cord is directly destroyed by the venom, but this is 

 not due to deficient circulation. In animals injected with small amounts of 

 the venom, the initial fall of blood pressure is soon restored to the normal, 

 but the animal is weak and helpless. On examining such an animal the ten- 

 don reflexes are feeble or altogether absent; skin and corneal reflexes are 

 abolished, even if the circulation and blood pressure are well kept up. 



In frogs the injection of the venom (o.oi gm.) into the dorsal lymph-sacs 

 gradually retards and then stops respiration. In 20 minutes it is absolutely 

 paralyzed and even stimulation of the central and of the divided sciatic nerve 



1 C. J. Martin. On the physiological action of the venom of the Australian black snake (Pseudechis 

 porphyriacus). Read before the Royal Society of New South Wales, July 3, 1895. 



