I have myself found that saliva, so far from losing its alkalinity by evaporation, has this quality increased, and am inclined to re gard the reaction as dependent on the pre sence of tribasic phosphate of soda (a salt re acting on test paper as an alkali), as has been stated by Enderlin.
Chemistry.—Berzelius estimates the solids of saliva at about 1 per cent. From the solid re sidue he extracted osmazome, an alkaline lac tate, and chlorides of potassium and sodium by digestion with alcohol. That portion which the alcohol left undissolved consisted of soda, mucus, and a peculiar animal tnatter, which has been called " salivary matter," or " ptyalin." The mucus can be separated from this salivary matter and soda by digestion in cold water, which dissolves the two latter. The mucus thus separated by Berzelius yielded on in cineration a large proportion of phosphate of lime.
The following is his analysis of saliva :— Tiedemann and Gmelin obtained from 1.14 to 1.19 per cent. of solid residue by evapo rating saliva. From this, 0.25 parts of ash were obtained, of which 0.203 were composed of salts soluble in water, the remainder con sisting of earthy phosphates.
The following is a list of the constituents of the saliva, according to the above-men tioned chemists :— 1. Water.
2. A substance soluble in alcohol, and in soluble in water (fat containing phosphorus).
3. Matters soluble both in alcohol and water (osmazome, chloride of potassium, lac tate of potash, and sulpho-cyanuret of potas sium.
4. Animal matter soluble in boiling alcohol, but precipitated during cooling, with sulphate of potash and some chloride of potassium.
5. Matters soluble in water only (salivary matter with abundant phosphate, and some sul phate of an alkali, and chloride of potassium).
6. Matters soluble neither in water nor in alcohol (mucus, probably some albumen, with alkaline carbonate, and phosphate).
Mitscherlich gives the following analysis of the saline ingredients of saliva : Chloride of potassium - per cent. 0'18 Potash (in combination with 0'094 lactic acid) - - Soda - - - - - 0.024 Lactic acid - - - Soda (combined with mucus) - 0.164 Phosp1ate of lime - - - 0.017 Silica - - - - - 0.015 Siinon made an analysis of his own saliva, and gives the following as the result : Fat containing cholesterine - 0.525 Ptyalin with extractive matter - 4'375 Extractive matter and salts - 2.450 Albumen, mucus, and cells - 1.400 Water - - - - 991'225 Simon* adopted the following process in order to complete the above analysis. A
known weight of saliva was first evaporated to dryness ; the loss of weight thus indicated the proportion of water. The residue was treated with ether, which extracted the fats. The solid mass remaining was next treated with water, which dissolved out the ptyalin, extractive matters, and salts, leaving behind mucus, albumen, and cells.
Dr. Wright has experimented on saliva most industriously, and has entered at some length on the peculiarities of ptyalin, but evidently speaks of a very different constituent to that described by Berzelius and Simon. Accord ing to the mode of analysis adopted by these two latter chemists, the ptyalin of Wright will be estimated with the fatty constituents, among which it most probably holds its proper place.
His process of extraction is as follows :—" To pass saliva through ordinary filtering paper, and alter filtration shall have been completed, to exhaust the residue with sulphuric ether ; the ethereal solution contains a fatty acid and ptyalin. It is to be allowed to evaporate spontaneously, and the residue left by evapo ration is to be placed upon a filter and acted upon by distilled water, which dissolves the ptyalin and leaves the fatty acid. If the aque ous solution be carefully evaporated to dry ness, the salivary matter will be obtained in a pure state. Ptyalin, thus prepared, is a nearly solid matter, adhesive, and of a yellowish co lour ; it is' neither acid nor alkaline, readily soluble in ether, alcohol, and essential oils, but more sparingly soluble in water. It pos sesses the odour of saliva, and is precipitated by diacetate of lead, nitrate of silver, and slightly by acetate and nitrate of lead, and by tincture of galls ; neither bichloride of mercury nor the strong acids precipitate it. The latter de crease its solubility, and heighten its odour, while alkalies render it more soluble, and give it the odour of mucus. Ptyalin, when pure, may be kept a length of time, at a mo derate temperature, without undergoing de composition." According to Dr. Wright, saliva possesses the property of absorbing oxygen gas, and he states that he has known as much as 2.25 times the bulk of the saliva to be taken up. This quality varies, however, in different spe cimens; in Dr. Wright's opinion, according to the quantity of carbonic acid gas con tained in the secretion.