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 (5) 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 
