150 OF FOOD, AND THE DIGESTIVE PROCESS. 



is not entirely stopped, a small quantity of so-called paralytic saliva continu- 

 ing to be secreted when the tip of the tongue is excited by induced electricity. 

 The nervous circle stimulating the parotid glands to activity in the dog ap- 

 pears to be completed by the sensory fibres of the Glosso-pharyngeal and 

 gustatory of the Fifth, which transmit the impressions of taste to the Cerebro- 

 spinal nervous centres, from whence a motor impulse, inducing increased 

 secretory activity, is reflected through the Facial and the nervus petrosus 

 superficial is minor to the otic ganglion, and from thence to the gland through 

 motor fibres contained in the auriculo-temporal branch of the fifth. It is 

 possible also that the otic ganglion may be the centre of reflexion without the 

 cerebro-spiual centre being in any way implicated, the sensory impression 

 passing by the Glosso-pharyugeal and the nervus petrosus superficialis minor, 

 and being reflected at the ganglion upon the gland through the auriculo- 

 temporal. Section of the Nervus petrosus superficialis minor in the rabbit 1 

 causes an immediate increase of the flow of saliva from the parotid gland, 

 which lasts for ten minutes, and then subsides gradually, though it does not 

 entirely cease. Schiff believes it to be the vaso-motor dilator nerve of the 

 gland. Section of the Auriculo-temporal nerve, which is also a dilator nerve 

 for the vessels, abolishes the reflex salivation of the parotids. (SchifF, Ber- 

 nard.) Eekhard' 2 maintains that'in the sheep the Parotid glands act uniuter- 

 mittingly, and are not under the influence of any cerebral nerve, since no 

 change was effected in the secretion by stimulation of the fifth, or of the 

 portio dura of the seventh, or of the sympathetic nerve. Division of this 

 last in the neck was also devoid of influence, and no increase in the quantity 

 discharged was produced by brushing the mucous membrane of the mouth 

 with vinegar. Ludwig has pointed out, and this is an extremely important 

 point in the physiology of secretion, as showing the direct influence of the 

 nervous system upon gland tissue and cells apart from any action on the 

 bloodvessels, that if the circulation be suppressed and either the sensory 

 or excito-secretory nerves be irritated, a considerable amount of Saliva is 

 secreted. He also observed a fact which tells in the same direction, namely, 

 that the pressure under which the saliva is secreted by the submaxillary 

 glands as measured by a canula attached to a manometer, and introduced 

 into Wharton's duct, is greater than the pressure of the blood in the carotids. 

 In the former amounting to 190 mm. of mercury (or nearly 8 inches), whilst 

 in the latter it was only 108.5 112.3 mm. (or about 4 in.). The tem- 

 perature of the saliva he found to be 1.5 C., or nearly 3 F. warmer than 

 the blood of the Carotid artery. The partial independency of secretory ac- 

 tivity upon increased flow of blood through the gland is further shown by 

 the experiments of Giaunuzzi, 3 in which the glands were paralyzed by the 

 injection into the ducts of a 4.9 per cent, solution of Carbonate of Soda, or 

 of a 0.5 per cent, solution of hydrochloric acid. On stimulating the chorda 

 tvmpani all the ordinary vascular phenomena made their appearance, but 

 no increase in the amount of saliva secreted occurred and the gland soon 

 became oedernatous, the fluid which should have been used up in the forma- 

 tion of saliva apparently accumulating in the lymphatic system. Obviously, 

 therefore, secretion is not a purely physical action ; and as Ranke 4 remarks, 

 although a large supply of blood affords abundant material for secretion, it 

 is requisite before this act can be accomplished that some change should occur 

 in the gland cells themselves, which it is the special province of the nervous 



1 Schiff, Lemons sur la Physiol. dc la Digest., 1867, p. 228. 



2 Henle and Pfeuffer, Zeits., Bd. xxix, 1S07, Hct't 1, p. 74. 



3 Ber d. k. sachs Gcsolls. d. Wiss., lS(>f>, p. 68. 



4 Grundzuge der Physiologic, 1868, p. 181. 



