418 CONSIDERATION OF CARBON COMPOUNDS. 



Proteolytic or Hydrolytic ferments. Enzymes. Proteolysis 

 is the change effected in proteids during their digestion, and as this 

 change in most cases is accompanied by the taking up of water, the 

 terms proteolytic or hydrolytic ferments are used for the substances 

 causing the digestive changes. They are also called enzymes, to 

 distinguish them from organized ferments, such as yeast and bacteria. 

 The composition of these compounds is not definitely known, but is 

 similar to that of proteids. Enzymes are present in many secretions 

 and are produced within the body. They are soluble in water and 

 glycerin, but insoluble in alcohol. They act only in the presence of 

 water. They have no power of reproduction and are apparently not 

 diminished in quantity by activity. Each ferment acts upon certain 

 groups of compounds, causing them (in most cases) to take up a 

 molecule of water. 



The most important of these unorganized hydrolytic ferments 

 are ptyalin, found in saliva ; pepsin and rennet ferment, found in 

 gastric juice; amylopsin, trypsin, steapsin, and a milk-curdling ferment 

 found in pancreatic juice ; invertin, found in intestinal juices ; and, 

 finally, a fibrin-forming ferment, found in coagulating blood. (Eor 

 details of most of these ferments, see next chapter). 



Pepsin is one of the active principles of gastric juice, capable of 

 converting albumin, in the presence of hydrochloric acid, into soluble 

 peptones. While pure pepsin is not known, a number of preparations 

 containing more or less of this ferment are sold as pepsin. They are 

 obtained by different processes of extraction from the glandular layer 

 of fresh stomachs from healthy pigs. 



Pepsin, U. S. P., should be either a fine, white, or yellowish -white, 

 amorphous powder, or consist of thin, pale yellow or yellowish, 

 transparent or translucent grains or scales. It should be capable of 

 digesting not less than 3000 times its own weight of freshly coagu- 

 lated and disintegrated egg-albumin. Saccharated pepsin, U. S. P., 

 is a mixture of 10 parts of pepsin and 90 parts of sugar of milk. 



Experiment 62. Use the U. S. P. process for the valuation of pepsin, as fol- 

 lows : Prepare, first, the following three solutions : A. To 294 c.c. of water add 

 6 c.c. of diluted hydrochloric acid. B. In 100 c.c. of solution A dissolve 0.067 

 gramme of the pepsin to be tested. C. To 95 c.c. of solution A, brought to a 

 temperature of 40 C. (104 F.), add 5 c.c. of solution B. The resulting 100 

 c.c. of liquid will contain 0.21 gramme of HC1, 0.00335 gramme of pepsin, and 

 98 c.c. of water. 



Keep an egg in boiling water for fifteen minutes ; rub the coagulated albumin 

 through a No. 30 wire sieve, place 10 grammes of this albumin in a 200 c.c. 



