PRACTICAL EXERCISES 455 



extract of stomach. Filter the contents of these lest tubes. Neutralize 

 the nitrate 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 8 (d) (p. 452) . 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. 353, 415). 



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

 starch mucilage, which has been previously found free from reducing 

 sugar. Put in a bath at 40 C. After a short time abundance of 

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

 amylopsin, or pancreatic amylase. 



(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 chloro- 

 form 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 bzen 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 

 overnight. 



(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* 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 drop or two of litmus solution, and, if 

 necessary, enough of dilute sodium hydroxide to just establish a blue 

 colour. Then put the test-tubes at 40 C., and examine after a time. 

 No digestion will have taken place in A, because the pancreatic juice, as 

 secreted, does not contain active trypsin. In B digestion may take 

 place, because the enterokinase in the intestinal mucous membrane 

 will activate the trypsinogen to trypsin. In C and D there will be 

 evidence of the production of reducing sugar and fatty acids respec- 

 tively, since the pancreatic juice, as secreted, contains active amylase 

 and steapsin. E will be unchanged unless by bacterial action. 



(/) Leucin and Tyrosin. As examples of amino-acids formed when 

 pancreatic digestion of proteins (fibrin or cassin, e.g.] is allowed to go 

 on for some days.fleucin and tryosin maybe isolated. Add bromine- 

 water by drops to 5 c.c. of the digest; a pink colour indicates trypto- 

 phane. If the ' digest ' be neutralized, then filtered, and the filtrate 

 concentrated and allowed to stand, a crop of tyrosin crystals will 

 separate out, since tyrosin is only slightly soluble in watery solutions 

 of neutral salts. These crystals having been filtered off, the proteoses 

 (albumoses) and peptones can be precipitated together by alcohol, and 



* 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. 401). 



| A little chloroform is added to prevent bacterial growth. 



