DIGESTION. 



potassium in the mixed saliva can be demonstrated by the 

 addition of a per-salt, especially the perchloride, of iron. 

 That this is a constant and normal ingredient of the human 

 saliva cannot be doubted. We have frequently had occasion 

 to apply this test to the saliva of different persons, and the 

 results have been invariably the same. The peculiar reaction 

 of the saliva with the perchloride of iron was first noticed by 

 Treviranus, who called the substance producing it blood-acid. 

 At the time this observation was made (1814), sulpho-cy- 

 anic acid had not been described. Tiedemann and Gmelin 

 confirmed this observation, and demonstrated the presence 

 of a sulpho-cyanide by other tests. 1 



It has been a question whether the red color produced by 

 the perchloride of iron be really due to the presence of a 

 sulpho-cyanide in the saliva ; or, if it exist at all, whether 

 this salt be a normal constituent, or be developed accident- 

 ally as a pathological condition, or produced, as has been 

 suggested, by the action of reagents. The elaborate investi- 

 gations of Longet seem to have settled these questions con- 

 clusively. He obtained nearly three quarts of human saliva, 

 which he collected in half an hour from forty soldiers, fast- 

 ing, who, after having rinsed and cleaned the mouth, excited 

 the secretion by chewing pieces of India rubber. The fluid 

 was then concentrated so that all the sulpho-cyanide was 

 brought into a few drops, which showed, to an intense de- 

 gree, the peculiar reaction with the perchloride of iron, By 

 suitable manipulations, the presence of sulphur was also es- 

 tablished. 2 



1 TIEDEMANN ET GMELIN, Recherches Experimentales, Physiologiques ct Chi- 

 miques sur la Digestion, Paris, 1827, premiere partie, p. 9 et seq. 



2 LONGET, Traite. de Physiologic, Paris, 1861, tome i., p. 160. In these ma- 

 nipulations, Longet followed the process of Tiedemann and Gmelin (he. cit.), 

 whose observations on this point were simply confirmed; the difference being that 

 in the observations of Longet the extract was made from a very large quantity 

 of saliva. It is unnecessary to review the process by which it is demonstrated 

 that the reaction with the perchloride is not due to the presence of the acetate 

 of soda, as has been suggested. 



