THE GASTRIC JUICE. 71 



saliva with a few drops of a strong solution of albumin. Use for 

 an indicator two or three drops of tropseolin, which turns red 

 with free acid, but remains yellow if the acid is combined with 

 a proteid. To each tube add very dilute hydrochloric acid, to the 

 first enough to produce a permanent red color, to the second not 

 enough for this. Try their digestive power on starch as before. 

 The trace of free acid has destroyed the enzyme; the acid com- 

 bined with the albumin hinders digestion but does not wholly 

 prevent it. 



178. In each of a series of test-tubes place 2 to 3 cubic centi- 

 meters of saliva, add half as much of the starch solution and a 

 few drops of the following antiseptics: Chloroform, sodium 

 fiuorid, salicylic acid, alcohol, mercuric chlorid, copper sulphate. 

 Let the tubes stand in water at 38 , occasionally removing a drop 

 and testing this for unaltered starch with iodin solution. Since 

 mercury salts form a compound with iodin it will be necessary to 

 use more of the reagent in this instance. When no more remains 

 Trommels test will show the presence of maltose. The antisep- 

 tics do not prevent digestion except the metallic salts which unite 

 with the albuminous substances. 



THE GASTRIC JUICE. 



The gastric juice, secreted by the glands of the stom- 

 ach, differs from the other digestive fluids in having an 

 acid reaction. It is a clear, thin liquid containing, as in- 

 organic constituents, principally the chlorids and phos- 

 phates of the alkalies and of calcium and magnesium. 

 There is more hydrochloric acid than can unite with the 

 bases, and this must consequently he in the free state. The 

 most important of the organic substances are two enzymes, 

 or unorganized ferments: pepsin and rennin. 



The acidity of the gastric juice is caused principally 

 by the free hydrochloric acid, but may be at times due 

 to the acid phosphates, or to the organic acids: lactic, 

 butyric, and acetic. The hydrochloric acid and acid phos- 



