CHANGES OF FOOD IN THE ALIMENTARY CANAL. 151 



system to induce. Heidenhain 1 has described at length the changes which 

 take place in the salivary glands which have been excited to secrete for a 

 considerable time by irritation of their nerves. These changes consist in the 

 breaking down of the large salivary cells to furnish the secretion, and their 

 replacement by a growth of small granular cells, which he believes to take 

 place from the protoplasmic "demilune" of Giannuzzi (cc, Fig. 61); Ranvier,' 2 

 however, whilst admitting that the secretion proceeds from the large cells, 

 maintains that they do not entirely break down, but merely yield up their 

 contents, their nuclei and the protoplasm surrounding the nuclei remaining 

 to repair the loss. 3 



The several conditions under which a flow of saliva may be made to occur, 

 are 1. By the reflex action of the submaxillary and otic ganglia, and of 

 the cerebro-spinal centres, excited by impressions conveyed through the 

 glosso-pharyngeal and gustatory of the fifth, and taking effect through the 

 motor branches of the facial, running in the chorda tympani and auriculo- 

 temporal nerves. 2. By calling into play the muscles of mastication, the 

 effect being probably due to coincident excitation of the nerves supplying 

 the glands with those distributed to the muscles. 3. By mental stimuli, as 

 by the sight or thought of sapid food. 4. By poisons circulating in the 

 blood, as Camphor, Woorara, Chloroform, and the Salts of Mercury. 5. By 

 lesion of certain parts of the encephalon, as the floor of the fourth ventricle ; 

 by irritation of the upper extremities of the sympathetic or pneumogastric 

 nerves divided in the neck, or of the central extremity of the divided sciatic 

 nerve, 4 which is not due (entirely at least) to the effects of this irritation in 

 producing increase of blood pressure. 



106. On its entrance into the Stomach, the food is subjected to the oper- 

 ation of the Gastric Juice, which is secreted by the follicles in its walls, or 

 by a certain part of them. This follicular apparatus is extremely extensive, 

 and makes up the chief part of the thickness of the gastric mucous mem- 

 brane. If this be divided by a section perpendicular to the surface (Fig. 

 65), it is seen to be almost entirely composed of a multitude of parallel tubuli 

 closely applied to each other, their ccecal extremities abutting against the 

 submucous tissue, which here contains a considerable quantity of the un- 

 striated form of muscular tissue that constitutes the muscular layer of the 

 submucous tissue of Kolliker, and their open ends being directed towards 

 the cavity of the Stomach. Between the tubuli, bloodvessels pass up from 

 the submucous tissue, and form a vascular network on its surface, in the 

 interspaces of which the orifices of the tubes are seen (Fig. 66). These tubular 

 glands, the number of which is estimated by Sappey at nearly five millions, 5 

 do not everywhere present the same structure. In that which may be con- 

 sidered as their most characteristic form, and which presents itself over the 

 greater part of the area of the membrane, the wide open orifice leads to a 

 pit of no great depth (Fig. 67, a), lined by columnar-epithelium 6 resembling 



1 Studicn cles Physiol. Inst. zu Breslau, 18fi8, p. 1. 



2 Notes to the French translation of Prey's Histolog3 T , p. 439, quoted in Kiiss, Phy- 

 siol"gie, 1873, p. 265. 



3 See also for a similar view, Ewald, Centralblatt, 1870, p. 375. 



4 .See P. Grutzner, Pfliiger's Arehiv, Bd. vii, 1873, p. 522. Heidenhain has shown 

 that the fibres of the chorda tympani nerve exciting the submaxillary gland to in- 

 creased secretion, are distinct from the inhibitory vaso-motor fibres, since the ad- 

 ministration of atropine paralyzes the former, but leaves the latter functionally 

 intact. 



5 Henle, Anatomic, 18(52, p. 159. 



6 Heidenhain's Hauptzcllen (chief or principal cells) ; Rollet's adelomorphous 

 cells; Jukes's conical cells. See Jukes, in Centralblatt, 1872, No. 47. 



