PAPERS ON MEDICINE AND PUBLIC HEALTH 271 



Calculation — The indicator used reacts only with free 

 hydrochloric acid, hence the number of cubic centimeters 

 of N/10 sodium hydroxide used indicates the volume neces- 

 sary to neutralize the free hydrochloric acid of 10 c. c. of 

 gastric juice. To determine the data for 100 c. c. of gastric 

 juice multiply by 10. Occasionally in the fractional method 

 it is not possible to obtain 10 c. c. of a specimen in one or 

 more of the periods of aspiration. In this case use £> c. c. 

 of the gastric content and dilute to 10 c. c. with distilled 

 water and proceed as above. Multiply the results by 2 be- 

 cause a 5 c. c. dilution was used. The latter procedure gives 

 only approximate results, yet, an idea of the nature of the 

 curve is determined. 



TOTAL ACIDITY 



Principle — The indicator used is phenolphthalein. Since 

 the indicator reacts with mineral acids, organic acids, com- 

 bined acids, and acid salts, the values obtained represent the 

 total acidity of the solution. 



Procedure — To the titrated solution used above add 2 

 drops of phenolphthalein and titrate with N/10 sodium hy- 

 droxide until a faint pink color is obtained and persists for 

 about two minutes. Take the burette reading and calcu- 

 late for total acidity. 



Calculation — The number of cubic centimeters of N/10 

 sodium hydroxide used indicates the volume necessary to 

 neutralize the total acidity of 10 c. c. of the solution. To 

 determine the data necessary for 100 c. c. multiply by 10. 

 (It is customary to express the acidity in values per 100 

 c. c.) This product of acidity represents the total acidity 

 of 100 c. c. of the solution of that period. 



OCCULT BLOOD 



Guaiac method used : Introduce 1 c. c. of gastric con- 

 tents into a 10 c. c. test tube and acidify with 1 or 2 drops 

 of glacial acetic acid. From a previously prepared solu- 

 tion, consisting of a few Guaiac crystals and 95% alcohol 

 (about 6 c. c. vol.), add to the gastric contents in equal 



