2 THE SECRETIONS: 



when collected and allowed to rest in a cylindrical glass, it is 

 observed to yield a deposit of epithelium-scales and mucus- 

 corpuscles, while the supernatant fluid remains clear. When 

 perfectly normal, its reaction is alkaline ; it is devoid of taste 

 and odour, and, when observed under the microscope, is seen 

 to contain peculiar corpuscles, which differ very slightly in their 

 form from tumid mucus- corpuscles. The appearance presented 

 by human saliva taken from the mouth, when examined under 

 the microscope, is depicted in fig. 13. I have always observed 

 the cells (a) in the saliva ; they appear to consist of swollen sali- 

 vary corpuscles. The salivary corpuscles are represented in (b) ; 

 (c) represents epithelium-scales ; and (d) fat-vesicles. Mem- 

 branous shreds are sometimes observed, apparently fragments 

 of injured epithelium-scales. 



The amount of solid residue in the saliva is very small; 

 it is composed of fat, ptyalin, water- extract, spirit-extract, a 

 little albumen, certain salts, and a trace of sulphocyanogen. 

 The presence of the last constituent was first noticed by 

 Treviranus ; it has since been detected by Gmelin and Tiede- 

 mann, and other chemists. 1 



The salts of human saliva are, according to Mitscherlich, 

 chloride of calcium, lactates of soda and potash, soda either 

 free or combined with mucus, phosphate of lime, and silica : 

 according to Gmelin and Tiedemann, they consist of alkaline 

 carbonates, phosphates, muriates, and traces of sulphates, toge- 



1 The occurrence of this substance in the saliva is equally interesting in a physiolo- 

 gical and chemical point of view ; and it would be very desirable to establish its pre- 

 sence in an unquestionable manner by experiments on a large quantity of saliva. 

 Gmelin and Tiedemann (Die Verdauung nachVersuchen, vol. i, p. 9) formed an alcoholic 

 extract of saliva, and distilled the residue, after mixing it with phosphoric acid. The 

 fluid obtained by this distillation reddened litmus paper, after some days evolved an 

 odour of prussic acid, yielded a deep yellow-red colour on the addition of perchlo- 

 ride of iron, and precipitates on the addition of nitrate of silver and nitrate of 

 peroxide of mercury. On the addition of sulphate of iron and sulphate of copper to a 

 portion of the distilled fluid, a white precipitate was thrown down, which communi- 

 cated a red colour to an acid solution of perchloride of iron. The clear chlorine- 

 solution, obtained by mixing chlorate of potash, hydrochloric acid, and chloride of 

 barium, was rendered turbid when digested with a portion of the distilled fluid, and 

 there was a gradual deposition of sulphate of baryta, the sulphuric acid being obtained 

 at the expense of the hydrosulphocyanic acid. Gmelin and Tiedemann observed the 

 reaction indicating the presence of sulphocyanogen in the saliva of the sheep, and 

 I have noticed it in the saliva of the horse. 



