72 PHYSIOLOGY CHAP. 



better on pricking the bulb in the vicinity of these centres, 

 secretion is at once aroused. 



Kohnstamm (1902) found that division of the nerve fibres that 

 arise in the chorda tympani and pass by the lingual to the sub- 

 maxillary gland, was followed by degeneration of a group of cells 

 in the bulb near the facial nucleus, mostly on the opposite side, to 

 a less extent on the same side as the operation. The nerve fibres 

 that come in the submaxillary gland originate in these cells. 

 Hence the latter are termed by the author the salivatory 

 nucleus. 



The interpretation of the effects of the so-called scialagogues is 

 doubtful. These consist in a series of toxic or medicinal substances 

 which, when injected under the skin or into the veins, promote a 

 more or less copious secretion of saliva. The principal are pilo- 

 carpine, physostigmine or Calabar beans, curare, etc. Do these 

 substances induce a flow of saliva because they directly or reflexly 

 excite the secretory nerves, or because they act by modifying the 

 metabolism of the secretory cells ? It is probable that their action 

 is distributed throughout the system, and that the effect is 

 analogous to the secretion of saliva produced in asphyxia by the 

 accumulation of carbonic acid and the other katabolic products 

 of metabolism in the blood. 



As contrasted with the substances which produce ptyalism, we 

 have another group, headed by atropine and daturine, which 

 arrest all salivary secretion (Keuchel). These substances act 

 particularly by paralysing the cranial secretory nerves. The flow 

 of saliva excited by pilocarpine can be arrested by atropine, and, 

 vice versa, the arrest of secretion by atropine can be antagonised 

 by pilocarpine and also by muscarine. 



The process of secretion, more particularly in the submaxillary 

 gland, which is the most accessible to experiment, has from 1851 

 to the present day been the subject of constant and varied experi- 

 ments (especially by Carl Ludwig and his school) which have 

 yielded very important results. The most significant of these data 

 and the deductions to which they lead can be summarised as 

 follows : 



(a) If after introducing a cannula into Wharton's duct in the 

 dog, the lingual branch of the fifth nerve (or simply the chorda 

 tympani, which runs from the facial to the lingual branch and 

 gives off fibres to the gland) is cut, all salivary secretion ceases, 

 and no saliva flows from the end of the cannula (Ludwig). This 

 proves that secretion of saliva is normally dependent on a reflex 

 nervous act conveyed to the gland by the fibres of the chorda 

 tympani. If the peripheral end of the lingual nerve (or the 

 chorda tympani) be electrically excited an abundant secretion of 

 saliva follows, which will in a few minutes reach, and even exceed, 

 the volume of the gland (Ludwig). This shows that stimulation of 



