186 LABORATORY WORK ON GASTRIC DIGESTION. [BOOK II. 



the fundus, (2) taken from the middle of the greater curvature, 

 (3) taken from the pylorus." 



9. Experiments on Pepsinogen and Pepsin; on Rennet Zymogen 

 and Rennet Ferment. 



The following experiments are taken from Langley's Directions for his 

 Practical Advanced Classes : 



(1) "Preparation of Extracts containing Pepsin and Pepsinogen. 

 Prepare an aqueous extract of a fresh gastric mucous membrane from a 

 hungry animal. 



The stomach should be taken as soon as possible after the death of the 

 animal and washed with solution of Na 2 C0 3 (O01 p.c.), chopped up, placed 

 in a mortar with about 120 c.c. of water, and repeatedly ground. In half- 

 an-hour to an hour the extract may be strained and filtered. Take 50 c.c. 

 of the filtered extract, add 5 c.c. HC1 1 p.c. Warm for half-an-hour, 

 neutralise with a? c.c. of 0-2 p.c. solution of Na 2 CO 3 . Label this Pepsin- 

 extract. Take 50 c.c. of the filtered extract, add to it a mixture of 

 5 c.c. HC1 (1 p.c.) and x c.c. Na 2 C0 3 . Label this Pepsinogen-extract. 



" (2) Effect of .N"a 2 C0 3 on Pepsin. 

 " Take 



Pepsin w , Sol. of Na 2 C0 3 



extract. (2 p.c.). 



a. 5 c.c. + 5 c.c. + neutral. 



b. + 4 c.c. + '5 c.c '1 p.c. Na 2 CO 3 . 



c. ,, + Oc.c. + 5 c.c 1 p.c. Na 2 C0 3 . 



" Shake and leave for 5 minutes. 



"Mix in three other test-tubes; x being the number of c.c. of HC1 

 required to neutralise 5 c.c. of Na 2 CO 3 (2 p.c.). 



Sol.ofNa 2 C0 3 HC1(lp>c) 



a '; A 5 , c ' c * + x ) fill up each to 15 c.c. with 



*/ ^ c ' c - water. 



c'. + x ) 



"Add a', b', c' to a, 6, c respectively; each should now be neutral. To 

 10 c.c. of each mixture add 5 c.c. HC1 ('6 p.c.) and 2 c.c. swollen carmine- 

 stained fibrin. Place at 39 C. and observe the rate of solution of the 

 fibrin. In a the solution will be rapid, less rapid in b, very slow in c, 

 shewing that pepsin is rapidly destroyed by sodium carbonate (1 p.c.). 



" 3. Pepsinogen. Repeat the previous experiment, using the pepsin- 

 ogen extract instead of the pepsin-extract. There will be very little differ- 

 ence in the rates of digestion in a, b, and c, probably it will be rather 

 slower in c than in the other two. This may arise either from a slight 

 destruction of pepsinogen, or from a destruction of pepsin formed in pre- 

 paring the extract, or possibly of pepsin originally present in the gastric 

 mucous membrane. 



