CHAP. XIL] OF DIGESTION. 179 



palmipedes, birds, carnivorous cetaceans). It is, on the contrary, 

 very abundant in the granivorous and herbivorous animals. 

 Schultz observed in a horse that a single parotid gland produced 

 in twenty-four hours 1,678 grammes of saliva. 



It is especially in the terrestrial vertebrates that the secretory 

 glandular apparatus exists well developed. It furnishes a liquid, 

 transparent, slightly viscous, usually alkaline, sometimes acid or 

 neutral. 



In the superior mammifers, and in man, there are three pairs 

 of salivary glands, called sublingual, submaxillary, and parotid. 

 Claude Bernard has shown that these glands do not secrete an 

 identical liquid. In effect ,the liquid secreted by the glandules 

 of the buccal mucous membrane seems incapable of transforming 

 starch into sugar, when it is blended with the parotidian saliva. 

 But it accomplishes very easily this transformation when it is 

 mixed with submaxillary saliva. 1 



The chemical agent of this isomeric transformation is a sort oi 

 special ferment, ptyaline. It is formed in the midst of the closed 

 cells which originate in the substances of the acini of the 

 gland ; these, breaking, surrender to the purely excretory liquid 

 the product of their elaborations. Thus we can easily obtain by 

 maceration of the glandular tissue an artificial salivation. 



The diversity of the products of secretion of glands in appear- 

 ance identical permits us to range in the category of the salivary 

 glands the venomous glands of serpents, which seem indeed to 

 form part thereof anatomically. The same reason authorises 

 us not to reject with too much disdain the facts, seemingly 

 ^legendary according to which the human saliva itself can 

 acquire venomous properties under the influence of a violent 

 burst of anger. The substances produced by living chemistry 

 ; undergo with an extreme facility isomeric metamorphoses : and 

 these metamorphoses bring along with them new properties. 



It is especially during mastication, when there is rapid contact 



1 Draper, loc. cit. p. 43. CL Bernard, Lefonssur les Liquides dc VOrganisme, 

 t. II., p. 239. " 



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