SECRETION 6i 



That of the colubrine forms (including the cobras) has, Hke 

 the saHvary secretion of the leech (hirudin) and mosquito, 

 anticoagulant action on the blood, and produces death chiefly 

 by asphyxiation through paralysis of the respiratory centre. 

 Cobra venom is also hsemolytic, i.e. it disintegrates the red 

 blood corpuscles. The venom of the viperine snakes (including 

 rattlesnakes) is also haemolytic, and differs from cobra venom 

 in the more marked local inflammatory reaction and the pre- 

 sence of a substance which promotes coagulation of the blood ; 

 its effect on the nerve centres is less marked. Alkaloids are 

 present in snake venoms, but their toxicity is slight. The 

 poisonous action is due to constituents of a simple protein- 

 like structure. Mammals may be artificially immunised by 

 injection of sublethal doses in increasing quantities. The 

 serum of animals so treated may be used as anti- toxin. It 

 is interesting to note that the blood of snakes (which are 

 immune to snake venoms), and that of animals like the hedge- 

 hog, which prey on snakes and also possess a high degree of 

 natural immunity, is toxic to animals which are relatively 

 susceptible to the poisonous effects of snake-bite. 



The phenomena of poison secretion are illustrated in all 

 large groups of the animal kingdom, and a more extensive 

 discussion would take us beyond the scope of the present 

 volume. 



Secretion o! Acids. — ^An aspect of the comparative physiology 

 of secretion which opens up a fascinating field for experimental 

 investigation that may throw light on the bionomics of some 

 boring animals is the production of strong acids by the diges- 

 tive glands of certain animals. More than half a century ago 

 Troschel noticed that the gasteropod, Dolium galea, squirts 

 from its mouth a liquid of strongly acidic reaction capable of 

 producing effervescence on coming into contact with the lime- 

 stone of the soil. This fluid is the secretion of the salivary 

 glands and contains as much as 4 per cent, free sulphuric acid 

 and about 0*5 per cent, hydrochloric acid. Schulz (1905) 

 has also studied the phenomenon of acid secretion in an opistho- 

 branch, Pleurobranchia meckelii. This animal not only 

 ejects an acidic fluid from its pharynx but produces with its 



