180 LABORATORY WORK ON GASTRIC DIGESTION. [BOOK II. 



" Take 



Ptyalin w Starch 



Solution. water> 3 p.c. 



(1) lOc.c. + 8c.c. + 2c.c. 



(2) + 3c.c. + + 5c.c. of HCl(0-2p.c.). 



(3) + Oc.c. + +2-5 c.c. HC1 (04 p.c.) + 5-5 c.c. sol. of pep- 



tone (10 p.c.) 



(4) + 3c.c. + +5c.c. Na 2 CO 3 sol. (0-2 p.c.). 



" (a) and (b) should be measured out in different sets of test tubes and 

 the (&)s added to the respective (a)s as nearly as possible at the same time. 

 (This should be done in all similar experiments.) 



" Place the test tubes in a water bath at about 39 C., and from time to 

 time take a drop from each, and add a drop of rather dilute iodine solution 

 on a porcelain plate. As the starch passes through soluble starch, and 

 dextrin to achro- dextrin and sugar, the colour of the mixed drops becomes 

 a transparent blue, then passes into violet, red-brown, light yellow, and 

 finally iodine gives no colour reaction with the solution. At any stage a 

 definite portion may be taken from each solution and tested for sugar. It 

 will be found that the conversion of starch to sugar is rapid in (1) and (3), 

 slower in (4) and hardly takes place at all in (2). In a similar way it may 

 be shewn that peptone saturated with acid almost or entirely prevents the 

 action of ptyalin on starch."] 



6. Determination of the amount of free Hydrochloric present 

 (Richet's 1 Modification of Schmidt's Method). 



Divide the gastric juice in four portions, which are to be accu- 

 rately weighed. 



a. In the first, determine the acidity expressed as HC1 by 

 titration with decinormal solution of soda. 



b. To the second, add pure nitric acid and then solution oi 

 silver nitrate. Collect the silver chloride, wash, dry, ignite, and 

 weigh, and thus determine the total chlorine. 



c. To the third, add a little sulphuric acid, evaporate to dryness, 

 ignite and weigh. Assume that the substance weighed, which con- 

 sists of the sulphates of all the bases present, is composed entirely 

 of sodium sulphate ; calculate on this assumption the amount o 

 sodium present, and therefore the amount of chlorine which would 

 be required to combine with the bases present on this assump- 

 tion. 



d. The fourth is mixed with a boiled out solution of potassium or 

 sodium hydrate, and placed under a bell-jar, together with a capsule 

 containing a measured volume of very dilute standard sulphuric 

 acid. After three or four days, the acidity of the standard acid is 

 determined, and from the diminution which has occurred, the amount 

 of ammonia which has been evolved by the gastric juice is ascer- 

 tained. 



1 Richet, Du Sue Gastrique, p. 33. 



