146 OF FOOD, AND THE DIGESTIVE PROCESS. 



According to the researches of Pfliiger 1 100 c.c. of the saliva of the dog 

 contains about 0.5 per cent, of its volume of oxygen, about 0.7 or 0.8 per 

 cent, of nitrogen, and from 49.2 to 64.7 per cent of carbonic acid, of which 

 one-third is free, whilst the rest is eliminated on the addition of phosphoric 

 acid. The substance to which the designation of ptyalin is given, is that on 

 whose presence the peculiar properties of the Saliva appear to depend; and 

 it seems, as regards its chemical nature, to be an albuminous compound, 

 since it coagulates by heat, nitric acid, and electricity; the precipitate is in- 

 soluble in water and in alcohol, but soluble in concentrated hydrochloric 

 acid with the production of a beautiful violet-red color, and it gives a violet 

 color when treated with sulphate of copper and caustic potash. A large 

 proportion of this albuminous substance is present in the saliva of the horse, 

 but only traces of it exist in that of man, and it appears to be in such a state 

 of unstable equilibrium that it acts the part of a "ferment." Potassium 

 Sulphocyanide, considered by Bernard 3 to be only occasionally present, and 

 attributed by some to the presence of carious teeth, and by others conceived 

 to have been mistaken for Nicotin, the essential oil of Tobacco, has been 

 found by Harley and Longet to be a constant constituent of the Saliva in 

 persons possessing perfectly sound teeth, and not addicted to smoking. It 

 is absent in the Saliva of the Herbivora. Its use may possibly be that sug- 

 gested by Kletzinsky, 4 to prevent the formation of fungoid spores between 

 and in the cavities of the teeth. In a medico-legal point of view, the exist- 

 ence of a sulphocyanide in the saliva has a special importance; since, if in a 

 state of sufficient concentration, it causes the saliva to exhibit the same 

 blood-red color, when treated with a persalt of iron, as that which is produced 

 by mecouic acid. (The difference between the two, however, is easily made 

 apparent, by adding a solution of perchloride of mercury; for this causes the 

 color produced by the sulphocyanide to disappear, whilst it has no action on 

 that which is due to the presence of mecouic acid.) To determine the nature 

 of the differences in the composition and physical characters of the secretion 

 of the several salivary glands, Bernard inserted tubes into their ducts, and 

 found, on placing a few drops of vinegar on the tongue of a dog, that the 

 submaxillary saliva was immediately secreted, speedily followed by that 

 from the parotid, and at a later period by that from the sublingual. The 

 parotidean saliva was clear and watery, with a specific gravity varying from 

 1003 to 1006, and containing only 0.47 per cent, of solid residue in the Dog, 

 and 0.76 in the Horse (Lehmann). The fluid discharged by the sublingual 

 gland was thick and viscid, whilst that of the submaxillary was intermediate 

 in this respect to the others, having a specific gravity of 1005. Hence Ber- 

 nard was led to suggest that the submaxillary gland ministers to the sense 

 of taste, whilst the parotid is connected with mastication, and the sublingual 

 with deglutition. The size of the parotid in animals is proportionate to the 

 degree in which the mastication of their food is performed. It is large in 

 the horse, which lives on comparatively dry food, less in caruivora, and 

 still less in the aquatic mammals, as the seal. It is absent in birds, which 

 swallow their food whole. 5 The submaxillary gland is largely developed in 

 the caruivora, but is again reduced to a minimum in birds. The Salts, ac- 





r's Archiv, Band i, 18f>8. p. 088. 



2 v. Wittich (Pflii^er's Archiv, Band iii, 1870, p. 330), in order to obtain it, recom- 

 mends tin 1 line! v-dividcd tissue to lie treated with absolute alcohol for 24 hours, after 

 which the residue is to he extracted with glycerin. Konuviti (Centralblatt, 1873, 

 p. 30-")) and Jul. Schift'er (Archiv f. Anat. v. Physiol., 1872, p. 464) show that it is 

 present in the saliva immediately after birth. 



3 Lecons, 1S59, t. ii, p. 243. 4 Heller's Archiv, 1833, p. 39. 

 6 Sue Hernard's Lectures, in the liev. Scientifiquc, 1873. 



