270 Comparative Physiology 



The venom glands of snakes are modified salivary glands. Leydig 

 noted a resemblance to the mammalian parotid glands, although in 

 most respects the structure seems closer to the salivary glands of 

 birds in that they have a loculated structure. The salivary duct 

 opens at the base of a grooved tooth which is the injection device; 

 the exact anatomical arrangement varies in different species. Ex- 

 pulsion of preformed secretion from the gland occurs as a result of 

 contraction of the gland or contraction of surrounding muscles. 



Snake venoms contain a great many enzymes (Zeller, 1948) some 

 of which are concerned with their toxicity. Phospholipase A 

 (lecithinase) seems to be the main heat-stable toxic factor in the 

 venom of water mocassins (Agkistrodon piscivorus) and rattlesnakes 

 (Crotalus terrificus). The rate of absorption of the toxin from the 

 site of injection is increased by the high concentration of hyalur- 

 onidase present. Especially high concentration of this enzyme is 

 present in the venom of vipers (V. aspis, V. riisselli, Echis carinata) 

 and the krait (Bungarus coerulens) (Deutsch and Diniz, 1956; 

 Hadidian, 1956; Jaques, 1956). 



Deutsch and Diniz (1956) point out that the venom from a 

 variety of snakes will form bradykinin from a serum globulin, in 

 the same way that saliva from many mammalian species will 

 (page 180). Viper venom also has prothrombin-like activity (Devi, 

 Bose and Sarkar, 1956) whereas cobra venom in the presence of 

 a plasma cofactor is an inhibitor of the conversion of prothrombin 

 to thrombin (Devi, Mitra and Sarkar, 1956). These also are rather 

 similar to the findings in mammalian saliva. 



The parotid glands of the toad have long been esteemed in China 

 under the name of Ch'an Su as a valuable ingredient of the pharma- 

 copoeia, used in many diseases but especially in cardiac failure. 

 Chen and his co-workers (Chen, Jensen and Chen, 1931) have 

 systematically studied the pharmacologically active materials in 

 toad glands (these have recently been reviewed by Jensen and 

 Westphal, 1956). These glands have as rich a collection of pharma- 

 cologically active substances as the octopus salivary gland. Con- 

 siderable amounts of adrenaline and noradrenaline are present as 

 well as the indolalkylamines, bufotenine (N-dimethyl-5 hydroxy- 

 tryptamine), bufotenidine (N-trimethyl-5 hydroxy tryptamine), 

 dehydrobufotenine (3-dimethylvinyl, 5 hydroxyindole) and bufo- 

 thionine (5-sulphatotryptamine). However, the most fascinating 

 substances present are a group of steroid glycosides with a highly 



