178 PHYSIOLOGY OF ALIMENTATION. 



upon in the way indicated suffers absolutely no inconve- 

 nience, if only care be taken to have the food fed the animal, 

 when not being used for experimental purposes, sufficiently 

 moist. 



2. The Relation of the Nerves to the Salivary Secretions. 

 Each of the three sets of salivary glands is supplied by two 

 sets of nerves, the one being of cranial origin, the other of 

 sympathetic. The submaxillary and sublingual glands are 

 supplied by a branch of the facial nerve the chorda tympani. 

 The parotid is supplied by the auriculo-temporal branch of the 

 trifacial nerve. The sympathetic fibres are derived in the 

 main from the second, third, and fourth thoracic nerves, 

 which, after passing into the sympathetic chain, ascend to 

 the superior cervical ganglion, from which nerve fibres, chiefly 

 of the non-medullated variety, are given off that, after follow- 

 ing the external carotid artery, are finally distributed to the 

 various salivary glands. Let us see now what the effect of 

 division and electrical stimulation of these various nerves is. 

 In spite of the many contradictory statements found in the 

 original papers of different investigators, these all seem to 

 agree on the following points. 



If a glass catheter is introduced into the duct of a salivary 

 gland, no or only very little secretion flows from it under 

 ordinary circumstances. If now the cranial nerve supplying 

 the gland is laid bare (for example, the chorda tympani nerve 

 to the submaxillary gland of a dog) and divided with a snip 

 of the scissors, no change occurs. Let, however, the peripheral 

 end of the divided nerve be stimulated electrically, mechani- 

 cally, or chemically, and the saliva is seen to move along the 

 catheter with increased rapidity. Soon a drop falls from its 

 end, and this is followed by _ another and another in rapid 

 succession. By far the most effective form of stimulation is 

 that with repeated induction shocks. A very weak current 

 will bring about such an increased flow of saliva, but within 

 certain limits the stronger the current the greater the flow 

 of saliva. Since the stronger currents injure the nerve, the 



