SALIVATION. 219 



always preceded by an increase of saliva. If a section of 

 the lingual be made, we find that irritation of the peripheral 

 part of the nerve which has been cut produces no effect on 

 the formation of the saliva, while excitation of the central 

 extremity, which is still connected with the spinal cord, is 

 certain to excite the secretion. The nerves which extend 

 from the bulb to the salivary glands, are fibres of the facial 

 nerve, especially the chorda tympani: this latter nerve be- 

 longs particularly to the sub-maxillary gland. 



Excitation of the great sympathetic nerv-e may also cause 

 secretion of the saliva, but this does not appear to take place 

 normally, under reflex influence. The saliva produced in 

 experiments, by the action of the great sympathetic nerve, is 

 much thicker than the normal saliva. This fact must be 

 compared with what takes place at the same time in the 

 vessels: when the great sympathetic nerve is excited the 

 vessels of the gland become constricted (contracted), while 

 the contact and exchange between the blood and the secre- 

 tory elements appear more intimate, since the blood which 

 flows from the gland is found to be quite black. On the 

 other hand, when the sub-maxillary gland secretes its fluid 

 products, under the influence of the facial nerve (chorda 

 tympani), we find the blood-vessels greatly dilated (para- 

 lyzed) and the blood which flows from them red, almost as 

 in the arterial system (Cl. Bernard). 



Too much importance must not, however, be ascribed to 

 the presence of the blood and the state of the vessels ; we 

 have already shown that the secretion of the saliva is an 

 instance of the immense attraction exercised by the secretory 

 globule over the surrounding substances. If the circulation 

 be suppressed, we may, by irritating the centripetal or cen- 

 trifugal nerves of the glands, cause the production of a 

 considerable quantity of saliva (Ludwig). The globule then 

 imbibes the materials for its support from the tissues which 

 surround it : it possesses great power of attraction, by which 

 it gives rise to the currents flowing towards it, across the 

 inert membrane which forms the coat of the secretory tubes. 



Thus the state of arterial pressure is only secondary. The 

 saliva is the result of a deliquium. of the cellular elements of 

 the glandular epithelium, and in this case we cannot con- 

 sider the gland as a mere filter. 1 This deliquium is pro- 



1 V. Billet, " Generalites sur les Secretions." These de Stras- 

 bourg, 1SG8, No. 129. 



