2l6 THE PAROTID SALIVA. 



[Excretion by the Saliva. Some drugs are excreted by the saliva. Iodide of potassium is 

 rapidly eliminated by the kidneys, and by the salivary glands, and so also is iodide of 

 iron. ] 



Theory of Salivary Secretion. Heidenhain has recently formulated the following theory 

 regarding the secretion of saliva : "During the passive or quiescent 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 secretion, and partly in the growth of the protoplasm. According to the 

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

 lated, 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 contain more 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 protoplasm ; hence, 

 the amount of organic constituents diminishes, and the microscopic characters of the cells are 

 altered. The microscopic characters of the cells are altered also by the increase of the pro- 

 toplasm, 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 pro- 

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

 protoplasm of the gland-cells." 



146. THE SALIVA OF THE INDIVIDUAL GLANDS. (a) Parotid saliva 

 is obtained by placing a fine cannula in Steno's duct; it has an alkaline reaction, but 

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

 C0 2 ; its specific gravity is 1003 to 1004. After standing it becomes turbid, 

 and deposits, in addition to albuminous matter, calcium carbonate, which is present 

 in the fresh saliva in the form of bicarbonate. It contains small quantities (more 

 abundant in the horse) of a globulin-like body, and never seems to be without 

 CNKS, i.e., sulphocyanide of potassium (or sodium), which, however, is absent in 

 the sheep and dog. 



[The sulphocyanide gives a dark red colour (ferric sulphocyanide) with ferric chloride, and the 

 colour is discharged by mercuric chloride, but this is not the case with meconic acid, which 

 gives a similar colour-reaction.] 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). 



Amongst the organic substances the most important are ptyalin, a small amount 

 of urea, and traces of a volatile acid. Mucin is absent, hence the parotid saliva is 

 not sticky, and can readily be poured from one vessel into another. It contains 1 '5 

 to 1*6 per cent, of solids in man, of which 0'3 to 1*0 per cent, is inorganic. 



Of the inorganic constituents the most abundant are potassium and sodium chlorides ; then 

 potassium, sodium, and calcium carbonates, some phosphates, and a trace of an alkaline 

 sulphate. 



^ 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 constituents ; 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 decomposing saliva in carious cavities between the teeth. 



(b) Sub-maxillary saliva is obtained by placing a cannula in Wharton's duct ; 

 it is alkaline, and may be strongly so. After standing for a time, fine crystals of 

 calcium carbonate are deposited, together with an amorphous albuminous body. 

 It always contains mucin (which is precipitated by acetic acid) ; hence, it is usually 

 somewhat tenacious. It contains ptyalin, but in less amount than in parotid 

 saliva ; and, according to Oehl, only 0-0036 per cent, of potassium sulphocyanide. 



Chemical Composition. Sub-maxillary saliva (dog) : 

 Water, . 991*45 per 1000, 

 Organic Matter, 2*89 ,, 



Inorganic Matter, 5'66 * '*! ? a J?i an ^ P* 01 * , ~ . . i * 



( l'lo CaC0 3 , Calcium and Magnesium phosphates. 



