CHANGES OF FOOD IN THE ALIMENTARY CANAL. 413 



is interesting, not only because this is the only animal product in which this 

 substance is known to occur, but because the uniformity with which it makes 

 its appearance when searched for, would seem to indicate that it performs some 

 peculiar part in the operations to which the salivary fluid is subservient. More- 

 over, in a medico-legal point of view, the existence 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 per- 

 salt of iron, as that which is produced by meconic acid. (The difference be- 

 tween the two, however, is easily made apparent, by adding a solution of per- 

 chloride 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 

 meconic acid.) The Salts of the Saliva, with the exception of the foregoing, 

 seem to correspond closely with those of the blood; and its alkaline reaction 

 appears due, not to the presence of a free alkali, but to that of the basic phos- 

 phate of soda. The " tartar" which collects on the teeth consists principally of 

 the earthy phosphates, which are held together by about 20 per cent, of animal 

 matter; and the same may be said of the salivary concretions which occasionally 

 obstruct the ducts. 



438. From the experiments of MM. Magendie 1 and Cl. Bernard, 3 however, 

 on the secretions of the respective glands, as obtained directly from them- 

 selves by tubes passed into their ducts, it appears that their composition and 

 physical characters are by no means uniform. For the fluid of the parotid and 

 sublingual glands is clear, and as limpid and thin as water, and contains but a 

 small proportion of solid matters (not more than 0.47 per cent, in the dog, and 

 0.76 per cent, in the horse, according to Lehmann and Jacubowitsch) ; whilst the 

 fluid of the submaxillary is thick and viscid, resembling in color and consistence 

 ordinary simple syrup, and containing a far larger amount of solid matters, in 

 which the organic components, however, bear a smaller proportion to the salts, 

 than they do in the fluid of the other two glands. Now it has been observed by 

 Bernard, that the flow of saliva which takes place during mastication proceeds 

 almost entirely from the parotid and sublingual glands; whilst, during the act of 

 deglutition, when the tongue carries the bolus back into the pharynx, the secre- 

 tion of the submaxillary is the greatest. Hence it seems reasonable to conclude, 

 that the purpose of these secretions is not identical; that of the parotid and sub- 

 lingual being to saturate the food when mixed up with it in the act of mastica- 

 tion ; whilst that of the submaxillary seems rather destined to facilitate degluti- 

 tion. 3 The fluid which is secreted by the three principal glands, moreover, appears 

 (from the experiments of Magendie and Bernard) to be far less efficacious than 

 is the buccal saliva, in producing that chemical change in the food which it is 

 the peculiar attribute of this secretion to exert ( 439) ; whence it seems fair to 



tion by an alkali, the addition of a little acetic acid occasions a flocculent precipitate, 

 wliich readily dissolves in an excess of the acid. When boiled with hydrochlorate of am- 

 monia or sulphate of magnesia, the alkaline solution of ptyalki becomes very turbid ; it is 

 precipitated by tannic acid, bichloride of mercury, and basic acetate of lead ; but not by 

 alum, sulphate of copper, &c. The acetic acid solution is strongly precipitated on the 

 addition of ferrocyanide of potassium ; and when boiled with nitric acid, it yields a yellow 

 solution. By these reactions it is shown that ptyalin closely resembles both albumen and 

 casein, without being identical with either of them. 



1 "Rapport lu dans la seance de 1'Institut," Oct. 25, 1845. 



2 "Archives Generates de Medecine," 4ieme serie, torn. xiii. 



3 This idea of M. Bernard's was confirmed by the following experiments. He made an 

 opening into the oesophagus of a horse, from which he drew the alimentary bolus as it 

 descended ; and on weighing it, he found that by the imbibition of saliva it had increased 

 elevenfold. He next tied Wharton's duct, and found that the animal required 41 minutes 

 to masticate what had previously required only 9 minutes ; and the mass, when withdrawn 

 from the oesophagus, was covered with mucus and a glutinous fluid, the interior being dry 

 and friable, and the whole increased in weight only three and a half times. 



