THE PAROTID SALIVA. 291 



Theory of Salivary Secretion. Heidenhain has recently formulated the 

 following theory regarding the secretion of saliva : " During the passive or quies- 

 cent condition of the gland, the organic materials of the secretion are formed from 

 and by the activity of the protoplasm of the secretory cells. A quiescent cell, which 

 has been inactive for some time, therefore contains little protoplasm, and a large 

 amount of these secretory substances. In an actively secreting gland, there are 

 two processes occurring together, but independent of each other, and 

 regulated by two different classes of nerve-fibres ; secretory fibres cause 

 the act of secretion, while trophic fibres cause chemical processes within the 

 cells, partly resulting in the formation of the soluble constituents of the secre- 

 tion, and partly in growth of the protoplasm. According to the number of 

 both kinds of fibres present in a nerve passing to a gland, such nerve being 

 stimulated, the secretion takes place more rapidly (cerebral nerve) or more 

 slowly (sympathetic), while the secretion contains less or more solid constituents. 

 The cerebral nerves contain many secretory fibres and few trophic fibres, while 

 the sympathetic contains many trophic, but few secretory fibres. The rapidity 

 and chemical composition of the secretion vary, according to the strength of the 

 stimulus. During continued secretion, the supply of secretory materials in the 

 gland-cells is used up more rapidly than it is replaced by the activity of the pro- 

 toplasm ; hence, the amount of organic constituents diminishes, and the micro- 

 scopic characters of the cells are altered. The microscopic characters of the cells 

 are altered also by the increase of the protoplasm, which takes place in an active 

 gland. The mucous cells disappear, and seem to be dissolved after prolonged 

 secretion, and their place is taken by other cells derived from the proliferation of 

 the marginal cells. The energy which causes the current of fluid depends upon 

 the protoplasm of the gland-cells." 



The saliva is diminished in amount in man in cases of paralysis of the facial 

 or sympathetic nerves, as is observed in unilateral paralysis of these nerves. 



146. The Saliva of the Individual Glands, 



(a.) The Parotid Saliva is obtained by placing a fine cannula in 

 Steno's duct (Eckhard) ; it has an alkaline reaction, but during fasting, 

 the first few drops may be neutral or even acid on account of free 

 C0 2 (Oehl) its specific gravity is 1,003 to 1,004. When allowed to 

 stand it becomes turbid, and deposits, in addition to albuminous 

 matter, calcium carbonate, which is present in the fresh saliva in the 

 form of bicarbonate. 



Salivary calculi are formed in the ducts of the salivary glands, owing to the 

 deposition of lime salts, and they contain only traces of the other salivary con- 

 stituents ; in the same way is formed the tartar of the teeth, which contains many 

 threads of leptothrix, and the remains of low organisms which live in decom- 

 posing saliva in carious cavities between the teeth. 



It contains small quantities (more abundant in the horse) of a 



globulin-like body, and never seems to be without CNKS sulpho- 



cyanide of potassium (or sodium Treviranus, 1814), which, however, 

 is absent in the sheep and dog (Brettel). 



The sulphocyanide gives a dark red colour (ferric sulphocyanide) with ferric 

 chloride. It also reduces iodic acid when added to saliva, causing a yellow colour 

 from the liberation of iodine, which may be detected at once by starch (Solera). 



