APPENDIX TO DIGESTION. 



I. THE ACIDS IN THE GASTRIC CONTENTS. 



Normally hydrochloric acid to the extent of about -4 per cent, is 

 secreted by the gastric mucous membrane, but in disease it may be 

 absent and lactic acid may be found. 



Detection of the Acids. 



The presence of an acid in a solution is shown by the colour change 

 it produces in an organic dye-stuff or indicator. In pure aqueous solu- 

 tions mineral acids give a distinct colour change, organic acids give 

 a less distinct colour change. The colour change is masked in the 

 presence of proteoses and peptones which are present in the gastric 

 contents, owing to the combination of the acid with the protein in the 

 form of a salt, so that it is difficult to decide whether hydrochloric 

 acid, free or combined, is present or absent. A decision may be 

 arrived at by making use of a series of indicators : 



(a) methyl violet ; 



() methyl orange, or dimethylaminoazobenzene (Topfer's reagent) ; 



(<:) Congo red ; 



(d) Uffelmann's reagent 2 per cent, phenol treated with dilute 

 ferric chloride till of an amethyst-violet colour (it is used especially for 

 lactic acid, p. 112); 



(e) Gunzberg's reagent 2 gm. phloroglucinol, i gm. vanillin, 30 

 gm. absolute alcohol (it is used especially for hydrochloric acid). 



The test with Gunzberg's reagent is carried out thus : 

 About 10 drops of the solution are placed in a small basin, 2-3 

 drops of freshly prepared Gunzberg's reagent are added, and they are 

 evaporated very carefully over a small flame, oscillating the basin and 

 blowing upon the mixture. Charring must be prevented. 



The differences in the colours of the indicators under the various 

 conditions may be seen by carrying out the following six experiments 

 with 1-2 drops of each of the indicators : 



(1) 2 c.c. of 0*4 per cent, hydrochloric acid (the strength occur- 

 ring in gastric juice). 



(2) 2 c.c. of dilute lactic acid (8 c.c in 1000 c.c. water). 



(3) 2 c.c. of O'4 per cent, hydrochloric acid and 2 c.c. of dilute 

 lactic acid. 



(4) 2 c.c. of 0*4 per cent, hydrochloric acid and 2 c.c. of 2 per 

 cent. Witte's peptone solution in 5 per cent, sodium chloride solution. 

 (This is to simulate the products of gastric digestion.) 



(5) 2 cc. of dilute lactic acid and 2 c.c. of 2 per cent. Witte's 

 peptone solution in 5 per cent, sodium chloride solution. 



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