THE ACTIVE FORCES OF LIVING ORGANISMS 8i 



Investigation into the nervous mechanism governing Secretory 

 the secretory action of the submaxillary gland has ohemico- 

 revealed facts which, from the point of view of the nCTves^in 

 matters just discussed, are of considerable interest. mLmary 

 When food enters the mouth, the extremities of the ^^^^'^' 

 lingual and glosso-pharyngeal nerves which are con- 

 nected with taste, the former in the fore, the latter in 

 the hind part of the tongue, are stimulated.* As a 

 result of this, nervous impulses are carried along 

 these nerves, and finally reach the centres of taste 

 in the cerebral cortex. What paths they follow and 

 what connections they set up is as yet but partly 

 known. Simultaneously, however, other impulses 

 travel, it is supposed, down the chorda-tympanii- 

 nerve to the gland, and cause a dilation of its blood- 

 vessels and secretory activity. J The cortical percep- 

 tion of taste is not the most important part of saliva- 

 tion, and we must suppose that stimulative impulses 

 travelling to the centre in the medulla oblongata, § 

 which governs the secretory process, are in reality 

 more essential. Considerable doubt exists as to the 

 true origin of the chorda-tympani nerve. Some look 

 on it as arising in connection with the fifth, some as 

 being a branch of the seventh or facial nerve. The 

 lingual being a branch of the fifth, its relations to the 

 chorda-tympani would be more easy to explain on the 

 first hypothesis, but the evidence hitherto accumulated 



* Foster, loc. cit., p. 1403. f Ibid., p. 396. 



I Ibid., p. 399. § Ibid., p. 398. 



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