PRACTICAL EXERCISES 429 



excess of 0*05 per cent, hydrochloric acid ; to D i per cent, sodium 

 carbonate alone ; to E i per cent, sodium carbonate in which a few 

 drops of glycerin extract of pancreas have been previously boiled ; 

 to F glycerin extract and excess of 0*2 per cent, hydrochloric acid.* 

 Set up six test-tubes, A', B', C', D', E', F', in the same way, but 

 substitute a few drops of a solution of commercial pancreatin for the 

 glycerin extract. Set up two test-tubes as in experiment 4 (p. 426) 

 with Mett's tubes. Put all the test-tubes in a tumbler, and place in a 

 bath at 40 C. The fibrin will be gradually eaten away in A and A', 

 by the action of the trypsin, but will not swell up or become clear 

 before disappearing, as it does in dilute hydrochloric acid with 

 glycerin extract of stomach. Filter the contents of these test-tubes. 

 Neutralize the filtrate with dilute acid ; a precipitate will consist of 

 alkali-albumin. If such a precipitate is obtained, filter it off and test 

 the filtrate for proteoses and peptones as in 4 (d) (p. 426). Some 

 digestion, and perhaps a considerable amount, may also have taken 

 place in F and F' ; less or none at all in C and C ; and none in the 

 other test-tubes (pp. 331, 394). 



(c) Add a few drops of the glycerin extract to a test-tube con- 

 taining starch mucilage, which has been previously found free from 

 reducing sugar. Put in a bath at 40 C. After a short time abund- 

 ance of reducing sugar will be found, owing to the action of the 

 ferment, amylopsin. 



(d) Mince thoroughly a good-sized piece of fresh pancreas, and 

 shake up well with three or four times its bulk of water. Put 5 c.c. 

 of fresh cream into a test-tube, then 10 c.c. of the extract, a few 

 drops of chloroform to prevent the growth of bacteria, a few drops 

 of litmus solution, and if necessary enough of very dilute sodium 

 hydroxide to just render the colour distinctly blue. Shake up, and 

 divide the mixture into two portions, A and B. Boil one portion (B), 

 and place the test-tubes at 40 C. Examine from time to time. The 

 blue colour will disappear in A, owing to the formation of fatty acids 

 from the neutral fats, and sodium hydroxide must be added to it to 

 restore the colour. In B the fat-splitting ferment has been destroyed 

 by boiling, and fat-splitting will not occur. Probably a distinct 

 result will not be obtained for several hours, and it will be best to 

 leave the tubes in the incubator over-night. 



(e) If the laboratory possesses an animal with a pancreatic fistula, 

 the following experiment may be done by a limited number of 

 students with fresh pancreatic juice f collected from the fistula. 

 Take five test-tubes, A, B, C, D, E. Add 5 c.c. of pancreatic juice 

 to each tube. Boil E, and then cool it. Put into A and B small 

 pieces of heat-coagulated egg-white, into C a little starch mucilage, 

 and into D and E 5 c.c. of fresh cream. Add further to B a scraping 

 of the mucous membrane of the upper part of the small intestine 

 which has first been washed free of contents. To D and E add a 



* With hydrochloric acid of different strengths the rapidity of digestion 

 of boiled fibrin by glycerin extract of dog's pancreas (i volume of extract 

 to 25 of acid) was found about the same for 0*3 and o'l/ per cent, acid ; 

 much less for o'o8 per cent., while in 0*04 per cent, acid there was prac- 

 tically no digestion at all. In o'4 per cent, acid digestion took place 

 more rapidly than in o'o8 per cent., but much less rapidly than in 0*17 per 

 cent. In acid of all strengths digestion was markedly slower than in 

 i per cent, sodium carbonate. 



f A considerable flow of pancreatic juice can be obtained from a dog 

 with a pancreatic fistula by injecting intravenously an extract of intestinal 

 mucous membrane containing secretin (p. 379). 



