CHAP. II.] IS ACID OF GASTRIC JUICE FREE HYDROCHLORIC ACID ? 95 



Benzo- A still more sensitive colour test is said to be fur- 



Purpurin. nished by benzo-purpurin, although the author cannot 



speak of it from his own experience. The following account is taken 

 from v. Jaksch. 



" Five milligrammes will serve to shew O39 milligrammes of acid 

 dissolved in 6 c.c. of water (Hellstrom), causing the dark-red colour of 

 the solution to give place to a light violet. A similar change is 

 effected with acetic, formic, and lactic acids ; but the colour obtained 

 with organic acids is rather a brownish- violet, and requires a greater 

 quantity of the latter for its production ; in the case of acetic acid, 

 not less than 0'84 milligramme. Test papers may be prepared by 

 soaking strips of filter paper in a saturated watery solution of benzo- 

 purpurin, and subsequently allowing them to dry. If one of these be 

 placed in gastric juice, it will immediatel} 7 stain a dark blue, provided, 

 hydrochloric acid be present in a proportion not less than 0'4 grm. to 

 100 c.c. A brownish-black tint maybe due to the presence of organic 

 (lactic or butyric) acids ; or from a mixture of these with hydrochloric 

 acid. The ambiguity in this case may be dispelled by placing the 

 paper so stained in a test tube and shaking it up with sulphuric ether, 

 when so much of the colour as is due to the presence of organic acid 

 will speedily disappear, leaving a lighter stain, or restoring the paper 

 to its original tint. If hydrochloric acid alone be present no change 

 will be effected in this way, and even after the lapse of twenty-four 

 hours the blue stain will be only slightly displaced 1 . 



Is the Acid of the Gastric Juice free Hydrochloric Acid ? 



The observations of Carl Schmidt proved that the gastric juice 

 contains a chlorine-containing acid uncombined with bases, and 

 taken in connection with the facts, firstly that the gastric juice 

 yields free hydrochloric acid on evaporation, secondly, that the 

 gastric juice yields the same reactions with certain reagents (methyl- 

 violet, Reoch's reagent, 00 tropaeolin) as a dilute solution of a mineral 

 acid, it would appear in the highest degree probable that the chlorine- 

 containing acid is in reality hydrochloric acid. 



It has however been maintained that in some particulars the 

 gastric juice does not behave exactly like a dilute solution of 

 hydrochloric acid of the same degree of acidity. Some of the sup- 

 posed points of difference depend however upon errors of observa- 

 tion, and others are explained by the modifying influence exercised 

 upon the hydrochloric acid by the organic matters of the gastric 

 juice. 



It was asserted by Blondlot that gastric juice does not decompose 

 calcium carbonate, and the supposed fact was used as an argument 

 in support of Blondlot's theory that the acidity of the gastric juice 



1 v. Jaksch, Op. cit., p. 99. 



