GASTRIC JUICE AND CHANGES IN STOMACH. l6/ 



mate this by aid of another indicator. Sodium alizarin sul- 

 phonate has been used for this purpose, but the reaction is not 

 as sharp as desirable. This substance appears to behave as a 

 weak acid, but one not as weak as phenol-phthalein. Lactic 

 acid may be titrated with it, but protein separated from HC1 

 behaves as a base toward it. Theoretically the three indica- 

 tors are related in this way, as illustrated by diagrams, in 

 which H Pht represents phenol-phthalein, HA1 alizarin sodium 

 sulphonate, Or Cl the hydrochloric acid salt of dimethylam- 

 inoazobenzene and HL lactic acid : 



H Pht "I HA1 ") Or Cl 1 



HC1 Prot. L I -M nw HC1 Prot - U_I_XT nw HC1 Prot - I \ XT nu 

 HL f+NaOH. RL H- NaOH. HL f+NaOH. 



HC1 J HC1 J HC1 J 



i 2 3 



It has been shown above how phenol-phthalein and the methyl 

 orange bodies act. The alizarin sulphonate as standing mid- 

 way between them in properties is influenced by the protein 

 which may be separated from acid albumin in titration with 

 NaOH. Therefore the difference between the titrations in 

 schemes numbers 2 and 3 must measure the lactic or similarly 

 acting organic acid. 



Under some conditions this appears to be true. When 

 there is relatively much lactic acid present and not much of 

 the digestion products a fairly good end reaction is obtained. 

 This corresponds of course to a practical case and the indica- 

 tor then has some value. But as digestion goes on the prod- 

 ucts formed are more or less basic. While not strong enough 

 to affect the phenol-phthalein they do appear to act on the 

 alizarin compound in such a manner as to diminish the alkali 

 required for titration ; the free hydrochloric acid is thus made 

 to appear low. It is plain that the indicator has but limited 

 value. 



The Amount of Pepsin. Thus far the detection and esti- 

 mation of the acid in the stomach contents has alone been con- 

 sidered, but the question of the amount of pepsin present may 

 be of equal importance. We have no very satisfactory tests 



