418 



SALIVA. 



The properties and physiological uses of 

 the saliva have been examined into by a great 

 number of observers, and we find much valu- 

 able and curious matter for consideration in 

 their general results. 



General Properties. Boerhaave and Hoff- 

 man ascribed a peculiar fermentative power 

 to saliva, a subject which was subsequently 

 more fully entered upon by Sir John Pringle 

 and Dr. Macbride. The former observer 

 experimented on certain anti-putrescent qua- 

 lities of the secretion, and found that raw 

 meat putrefied slower after admixture with 

 saliva. Another experiment of Sir John's 

 deserves description in detail. He took two 

 drachms of fresh meat, and the same quantity 

 of bread, and to these added as much saliva as 

 he supposed might be necessary for digestion. 

 He beat up this mixture in a mortar, then 

 enclosed it in a phial, and set it in a warm 

 atmosphere for about two days. No signs of 

 fermentation could be detected at the end of 

 that time, but during the third day the bread 

 and flesh rose in the water, a sediment 

 formed, and bubbles were observed mounting 

 in the liquor. The mixture now possessed a 

 vinous smell. This action was observed to 

 continue about twice as long as in a similarly 

 conducted experiment made without saliva. 

 In the former case the fermentation was more 

 gradual, and when complete the mixture 

 possessed a pure acid flavour, and had no 

 disagreeable smell. 



Notwithstanding that the subject has been 

 laboriously investigated by some of the most 

 ingenious experimenters of the day, the uses 

 of the saliva in the economy are evidently 

 still but imperfectly ascertained. Spallanzani 

 was inclined to believe in a solvent action 

 which this fluid was capable of exerting on 

 animal matters, and thought that food, when 

 inclosed in a tube perforated with numerous 

 small holes, and placed in saliva, was more ra- 

 pidly broken up and dissolved than when water 

 only was used. The further observations of 

 Berzelius and Miiller tended, however, to im- 

 pugn the correctness of this opinion, pure 

 water acting, according to their experiments, 

 quite as efficiently as saliva. 



Some experiments have been made by 

 Hiinefield, by which he thinks he has shown 

 saliva to possess a peculiar action on fibrin : 

 this, however, requires confirmation. In the 

 year 1831 Leuchs made a most important 

 discovery in connection with the history of 

 saliva, viz., that when boiled starch is added 

 to it, and the mixture is kept at a temperature 

 of 98, the starch becomes converted into 

 sugar. This action has been since investi- 

 gated by Mialhe, who attributes the pheno- 

 menon to the presence of a peculiar proximate 

 principle existing in saliva, to which he has 

 given the name of animal diastase, in con- 

 sequence of its possessing the qualities of 

 that principle as it exists in the vegetable 

 kingdom, in germinating seeds. In order to 

 obtain this substance the saliva is to be fil- 

 tered, and then precipitated by the addition of 

 absolute alcohol, of which generally from five 



to six times the weight of the saliva are re- 

 quired to effect the purpose. The animal 

 diastase falls in the form of a flocculent pre- 

 cipitate, which may be collected and dried on 

 a filter. It forms about 0*2 of the whole 

 saliva. It is a w r hite substance, insoluble in 

 alcohol. 



A series of experiments have been lately 

 made by M. Bernard, with a view of deter- 

 mining what the action of saliva may be in 

 the digestive process. 



He first satisfied himself that the saliva of 

 the horse and the dog, as well as that from the 

 human subject, possessed the property of de- 

 composing starch into sugar, under the con- 

 ditions of temperature above described. The 

 saliva of the dog, however, effected the con- 

 version but slowly, that of the horse more 

 quickly, but neither nearly with the rapidity 

 of human saliva. The dog's saliva required 

 nearly eight times as long as that from man, 

 and that of the horse nearly four times as 

 long. Care was taken in these experiments 

 to employ the same quantities of saliva and 

 of starch. 



Pure saliva, obtained from the parotid and 

 subrn axillary glands of the dog, were found 

 by Bernard quite incompetent to effect the 

 transformation of starch. This agrees with 

 the observation of Lassaigne, who found that 

 pure saliva from the parotid of horses pos- 

 sessed no transforming power of the kind, 

 though mixed saliva taken from the oesophagus 

 acted well ' on starch. According to Ber- 

 nard's experiments, the explanation of this 

 rests on the fact that the power of trans- 

 formation is a property of the secretion from 

 the mucous membrane lining the mouth, for 

 on placing layers of that membrane in contact 

 either with starch or sugar he obtained de- 

 composition, and lactic acid was produced. 

 He thus reduces the importance of saliva, as 

 an adjunct in digestion, to little more than 

 that of a lubricating fluid. 



Saliva of Animals. The saliva of animals 

 has not been much experimented upon. 

 Berzelius remarks as follows on the saliva 

 of the dog * : "As obtained from the pa- 

 rotid, it is a pale yellow fluid of mucila- 

 ginous consistence, resembling white of e<rg 

 in its physical characters. It leaves 2'o8 

 per cent, of solid matters on evaporation. 

 These solids form a transparent pale yellow 

 varnish on the surface of the evaporating 

 dish, which becomes moist by exposure 

 to air. Alcohol extracts principally chlo- 

 ride of sodium from this mass, and, by eva- 

 porating the alcoholic solution, crystals of 

 the chloride can be obtained nearly in a pure 

 state, being, however, mixed with a small 

 proportion of a yellowish substance, com- 

 posed principally of lactate of soda and os- 

 mazome. Sulphocyanogen cannot be de- 

 tected with certainty in the alcoholic extract, 

 and but a trace only of its reaction with the 

 salts of iron can be observed. 



The portion of solid matter which is in- 



* Traite de Cliimie, vol. vii. 



