of the Salivary Glands 27 1 



active cardiotonic effect. These fall into two classes, the free glyco- 

 sides with a six-membered lactone ring (identical to that in scil- 

 laridin A) called Bufogenins, and conjugates of these substances 

 with suberylarginine called Bufotoxins. The lethal dose in the cat 

 of bufalin is 137 //g/kg; this compares favourably in toxicity and 

 cardiotonic activity with the best of the plant glycosides. Chen 

 found similar activity in all species of Bufo although the chemistry 

 of the substances present is not identical. The function of these 

 substances is unexplained, but they are unlikely to be the source 

 of an internal secretion, since toads thrive after removal of the 

 parotid glands. It is possible that they are used offensively since 

 the material is toxic to a wide range of animals, but it is difficult to 

 see how they can constitute an effective venom in the absence of an 

 injection device. 



Birds have an elaborate system of salivary glands. Histologically 

 these glands are septate (Calhoun, 1932). There is a paucity of 

 physiological data on bird saliva, but presumably it has a lubricative 

 and digestive function. It is also used in nest building. The oriental 

 delicacy, birds' nest soup, is made from dried salivary mucin 

 obtained from the nest of the Borneo swift. 



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