GASTRIC DIGESTION. 49 



as a normal product formed during the digestion of a meal 

 rich in carbohydrates. 



The following experiments are designed to show the ordi- 

 nary tests for lactic acid and the effect upon the reliability 

 of these tests, of the simultaneous presence of bodies likely to 

 be found in a stomach contents. 



(a) To successive portions of 5 c.c. of Uffelmaris reagent 

 add a few drops of solutions a, c, and d, under Hydrochloric 

 Acid. Note carefully color changes and make deductions. 



Make a very dilute solution of Fe 2 Cl 6 in which the yellow 

 color is hardly visible. Such a reagent is much more sensi- 

 tive than Uffelman's. Use 5 c.c. of the dilute ferric chloride 

 solution in testing each of the following: 



(6) Solutions a, c, and d (under HC1). 



(c) A solution of H 2 NaP0 4 . 



(d) Alcohol, 5 per cent. 



(e) A 1 per cent solution of saccharose; glucose. 



Make deductions as to the value of the test applied 

 directly to gastric contents. 



In order that all chances for error may be avoided, lactic 

 acid can be easily separated from disturbing conditions by 

 shaking the stomach contents or gastric juice with ether in 

 which the acid is soluble. Such an ether extract is evapo- 

 rated carefully on the water-bath, the residue taken up with 

 water and tested with the dilute Fe 2 Cl 6 solution. 



As this ether extract cannot contain any of the above 

 substances, the presence of which in the stomach contents 

 might interfere with a correct diagnosis, a positive test for 

 lactic acid in this case is decisive evidence of its presence. 



PEPSIN AND PEPSINOGEN. 



Pepsin is apparently not secreted as such, but appears 

 first in the gastric mucosa in an antecedent form, or zymogen, 



