404 APPENDIX. 



(c) Prepare another tube and add a few drops of Millon's re- 

 agent. The albumen is coagulated, and, on boiling, turns red- 

 dish. If only a little proteid is present no coagulation will oc- 

 cur, but the mixture will redden when boiled. 



(d) Make the contents of another tube strongly acid with 

 acetic acid, then add a few drops of potassium ferrocyanide, and 

 a white precipitate will form. 



(2) Some of the chemical reactions of digested proteids (peptones). 



Make a peptone solution by dissolving some of Merck's pep- 

 tone in water. Repeat the experiments given for proteids. 

 Results similar to those in (b) and (c) will be obtained, but the 

 peptone does not coagulate on boiling, nor does it give the 

 white precipitate with acetic acid and potassium ferrocyanide. 



(3) To show that peptones are diffusible through membranes, 

 while proteids are not. 



Prepare the two dialyzers as for the experiments with starch 

 and grape-sugar. Into the inner jar of one dialyzer put some 

 of the white-of-egg mixture, and into the other some peptone 

 solution. After a few hours test the water in the outer jar of 

 each dialyzer. It will be found that the peptone passes through 

 the membrane, while the proteid does not. 



(4) To show that the gastric juice digests proteids i. e., changes 

 them to peptones. 



Prepare some artificial gastric juice as follows: Make some 

 .2 per cent, hydrochloric acid by mixing 5.5 cubic centimetres 

 of hydrochloric acid (sp.gr. 1.16) with enough distilled water 

 to make one litre. In 100 cc. of this acidulated water put 100 

 milligrammes of a, 6000 pepsin, or 150 mg. of a 4000, or 300 of 

 a 2000 pepsin. Any commercial pepsin may be used. Prepare 

 the proteid by boiling an egg, and then cutting the white into 

 small cubes or shreds. In place of the boiled egg some of 

 Merck's prepared fibrin may be used. 



With litmus paper test the reaction of the artificial gastric 

 juice. It will turn blue litmus paper red, thus showing that its 

 reaction is acid. 



Fill a test-tube about one-fourth full of the artificial gastric 

 juice, and add a few pieces of coagulated white of egg or of 

 fibrin; then set the tube in a warm place, as in a water bath 



