212 ACTION OF NERVES ON THE SECRETION OF SALIVA. 



Pfluger states, with regard to the latter, that (a) medullated nerve-fibres penetrate the acini ; 

 the sheath of Schwann unites with the membrana propria of the acinus ; the medullated fibre 

 still medullated passes between the secretory cells, where it divides and becomes non- 

 medullated, and its axial cylinder terminates in connection with the nucleus of a secretory cell. 

 [This, however, is not proved] (fig. 155, F). (6) According to Pfluger, some of the nerve-fibres end 

 in multipolar ganglion cells, which lie outside the wall of the acinus, and these cells send 

 branches to the secretory cells of the acini. [These cells probably correspond to the branched 

 cells of the basket-shaped structure.] (c) Again, he describes medullated fibres which enter the 

 attached end of the cylindrical epithelium lining the excretory ducts of the glands (E). Pfluger 

 thinks that those fibres entering the acini directly are cerebral, while those with ganglia in their 

 course are derived from the sympathetic system, [(d) The direct termination of nerve-fibres has 

 been observed in the salivary glands of the cockroach by Kupffer.] 



145. ACTION OF THE NERVOUS SYSTEM ON THE SECRETION OF 

 SALIVA. A. Sub-maxillary Gland. Stimulation of the facial nerve at its 

 origin causes a profuse secretion of a thin watery saliva, which contains a very 

 small amount of specific constituents. Simultaneously with the act of secretion, the 

 blood-vessels of the glands dilate, and the capillaries are so distended that the pulsatile 

 movement in the arteries is propagated into the veins. Nearly four times as much 

 blood flows out of the veins (CI. Bernard), the blood being of a bright red colour, 

 and containing one-third more O than the venous blood of the non-stimulated gland. 

 Notwithstanding this relatively high percentage of O, the secreting gland uses more 

 O than the passive gland (131, 1). 



[I Stimulation of Chorda. If a cannula be placed in Wharton's duct, e.g., in 

 a dog, and the chorda tympani be divided, no secretion flows from the cannula. 

 On stimulating the iieripheral end of the chorda tympani with an interrupted 

 current of electricity, the same results copious secretion of saliva and vascular 

 dilatation, with increased flow of blood through the gland occur as when the 

 origin of the seventh nerve itself is stimulated. The watery saliva is called chorda 

 saliva.] 



Two functionally different kinds of nerve-fibres occur in the facial nerve (1) 

 true secretory fibres, (2) vaso-dilator fibres. 



II. Stimulation of the sympathetic nerve causes a scanty amount of a very 

 thick, sticky, mucous secretion, in which the specific salivary constituents, mucin, 

 and the salivary corpuscles are very abundant. The specific gravity of the saliva 

 is raised from, 1007 to 1010. Simultaneously the blood-vessels become contracted, 

 so that the blood flows more slowly from the veins, and has a dark bluish colour. 



The sympathetic also contains two kinds of nerve-fibres (1) true secretory 

 fibres, and (2) vaso-constrictor fibres. 



[Electrical Variations during Secretion. That changes in the electromotive properties of 

 glands occur during secretion was shown in the frog's skin. Bayliss and Bradford find that the 

 same is true of the sub-maxillary gland (dog). During secretion, the excitatory change on 

 stimulating the chorda is a positive variation of the current of rest (the hilum of the gland 

 becoming more positive), but it is frequently followed by a second phase of opposite sign. The 

 latent period is always very short, about - 37". Atropin abolishes the chorda variation. On 

 stimulating the sympathetic, the excitatory change is of an opposite sign to that of the chorda, 

 and the hilum becomes less positive, so that there is a negative variation. It requires a more 

 powerful stimulus, is less in amount, and its latent period is longer (2"-4"), while atropin lessens 

 but does not abolish it.] 



Relation to Stimulus. Oh stimulating the cerebral nerves, at first with a weak and gradually 

 with a stronger stimulus, there is a gradual development of the secretion in which the solid 

 constituents occasionally the organic are increased (Heidenhain). If a strong stimulus be 

 applied for a long time, the secretion diminishes, becomes watery, and is poor in specific con- 

 stituents, especially in the organic elements, which are more atfected than the inorganic (C. 

 Ludwig and Becker). After prolonged stimulation of the sympathetic, the secretion resembles 

 the chorda saliva. It would seem, therefore, that the chorda and sympathetic saliva are not 

 specifically distinct, but vary only in degree. On continuing the stimulation of the nerves up to 

 a certain maximal limit, the rapidity of secretion becomes greater, and the percentage of salts 

 also increases to a certain maximum, and this independently of the former condition of the 

 glands. The percentage of organic constituents also depends on the strength of the nervous 

 stimulation, but not on this alone, as it is essentially contingent upon the condition of the gland 



