1 68 



PHYSIOLOGICAL CHEMISTRY 



free hydrochloric acid. The liberated iodine is titrated by thiosulphate 

 using starch as an indicator. It gives values similar to Topfer's re- 

 agent in average acidities. 1 Acidities other than free hydrochloric re- 

 act to a certain extent with Sahli's reagent, so that, for example, 

 high results are obtained after the ingestion of acid fruits. 



Procedure. Measure i c.c. of the strained stomach contents by means of an 

 Ostwald pipette and introduce it into a 60 c.c. porcelain evaporating dish. Dilute 

 with 10 c.c. of distilled water, and add i c.c. of Sahli's reagent (a mixture of 

 equal parts of 48 per cent KI and 8 per cent KIO 3 ). Allow the stomach contents 

 thus treated to stand for five minutes and then titrate with N/ioo sodium thio- 

 sulphate until only a faint yellow color remains. Now add 5-10 drops of a i 

 per cent solution of soluble starch and continue the titration until the blue color 

 disappears. In serial titrations the same procedure may be employed as de- 

 scribed on page 165, note 3. 



Calculation. Note the number of cubic centimeters of N/ioo sodium thio- 

 sulphate required to titrate i c.c. of stomach contents to the total disappearance 

 of blue color in the presence of starch. Inasmuch as N/ioo thiosulphate is 

 equivalent to N/ioo alkali, this value indicates the number of cubic centimeters 

 of N/ioo sodium hydroxide necessary to neutralize the free hydrochloric acid in 



FIG. 54. TOTAL ACIDITY AND PROTEIN CURVES IN BENIGN ACHYLIA (SOLID LINE 

 REPRESENTS ACIDITY). (Clarke and Rehfuss: Jour. Am. Med. Ass'n, 64, 1737, 1915.) 



i c.c. of the stomach contents. Multiply the value by 10 to obtain the number of 

 cubic centimeters of N/io NaOH necessary to neutralize 100 c.c. of stomach 

 contents. This is the method of calculation most widely used. For other forms 

 of expressing free acidity see page 177. Plot your results in a curve similar 

 to those shown in Figs. 49, 51, and 52, pages 153, 166 and 167. 



(c) Determination of Peptic Activity. (i) Method of Mett 2 as 

 Modified by Nirenstein and Schiff. 3 Principle. Small glass tubes 

 filled with coagulated egg albumin are introduced into the solution to 

 be tested, and kept for a definite length of time in the incubator. The 

 protein column is digested at both ends of the tube to an extent depend- 

 ing upon the amount of pepsin present. The method is not strictly 

 accurate but is the most satisfactory for clinical purposes on account 

 of its simplicity. Nirenstein and Schiff showed that human gastric 



, Bergeim and Hawk: Unpublished data. 

 2 Mett: Arch.f. Anat. u. Physiol., Verda 1894, 68. 

 'Nirenstein and Schiff: Arch.f. ankheruungsitekn, 8, 559, 1902. 



