1 70 PHYSIOLOGICAL CHEMISTRY 



(i) Controls of boiled gastric contents plus casein solution, and of distilled water 

 plus casein solution, treated as above stated, must show no digestion, and become 

 turbid on addition of the precipitating solution. 



(e) Detection of Lactic Acid. When the acidity of the stomach 

 contents is reduced to a low value there may occur considerable fermen- 

 tation of carbohydrates which have been introduced into the stomach 

 in the ingested food. This fermentation yields various organic acids 

 among which lactic acid is particularly prominent. It is important, 

 therefore, in case of low gastric acidity that the stomach contents be 

 examined for lactic acid. 



Tests, i. Ether -Ferric Chloride Test (Strauss). A satisfactory 

 deduction regarding the presence of lactic acid can only be made by 

 removing the lactic acid from disturbing factors (e.g., hydrochloric acid, 

 protein digestion products, etc.) present in the stomach contents. 

 Lactic acid may be extracted from the stomach contents by ether. 

 The following technic not only serves to detect lactic acid but also gives 

 an approximate idea as to the amount of the acid present. 



Procedure. Introduce 5 c.c. of strained stomach contents into a small grad- 

 uated separately funnel, add 20 c.c. of ether and shake the mixture thoroughly. 

 Permit the ether to separate, then allow all the fluid to run out of the separatory 

 funnel except the upper 5 c.c. of ether. To this ether extract add 20 c.c. distilled 

 water and 2 drops of a 10 per cent solution of ferric chloride and shake the mix- 

 ture gently. A slight green color is obtained in the presence of 0.05 per cent lac- 

 tic acid whereas o.i per cent lactic acid yields a very intense yellowish-green color. 



2. Ferric Chloride Test (Kelling). Fill a test-tube with water, add 1-2 

 drops of a 10 per cent solution of ferric chloride and mix thoroughly to form a 

 liquid which is very faintly colored. Divide the solution into two parts and keep 

 one part as a control. To the other part add a small amount of the strained 

 gastric contents and to the control tube add a similar volume of water. Lactic 

 acid is indicated by the immediate development of a distinct yellow color in the 

 tube containing the gastric contents. 



The color in this test is due to the formation of ferric lactate. 



3. Uffelmann's Reaction. To 5 c.c. of Uffelmann's reagent 1 in a test-tube 

 add an equal volume of strained gastric juice. A canary yellow or greenish- 

 yellow color develops if lactic acid be present to the extent of o.oi per cent or over. 



Other organic acid gives a similar reaction. Mineral acids such as 

 hydrochloric acid discharge the blue coloration leaving a colorless 

 solution. In other words, the color of the reagent is weakened in the 

 presence of an acid reaction. 



1 Uffelmann's reagent is prepared by adding ferric chloride solution to a i per cent solu- 

 tion of carbolic acid until an amethyst-blue color is obtained, due in part to the formation of 

 a ferric salt of carbolic acid and in part to the reduction of some of the iron. 



