1 68 PHYSIOLOGICAL CHEMISTRY. 



to determine this amount, but approximate values may be ob- 

 tained by observing the action of a filtered portion of the gas- 

 tric juice on some albumin solution to which weak hydro- 

 chloric acid has been added. Comparative tests may be made 

 in this manner: 



Prepare some egg albumin solution of about 2 per cent strength (2 per 

 cent of dry albumin) and mix this with 0.4 per cent hydrochloric acid in 

 equal proportions ; that is for every cubic centimeter of the albumin solu- 

 tion take one cubic centimeter of the acid solution. The resultant mix- 

 ture has an acid strength of 0.2 per cent and an albumin strength of i.o 

 per cent. Measure out 20 cc. of the acid-albumin mixture and add to it 

 5 cc. of the filtered gastric juice or stomach contents. To another 20 cc. 

 of the mixture add 5 cc. of a 0.2 per cent pepsin solution. Incubate both 

 mixtures through 24 hours at a temperature of 40 C, with frequent 

 shaking. At the end of the time examine both the incubated liquids for 

 digestion products. To this end neutralize a few cc. of each portion with 

 very weak alkali, using phenol-phthalein, and observe whether a precipi- 

 tate forms or not, directly or on warming gently. If no precipitate forms 

 in either fraction the digestion has gone beyond the acid albumin stage, 

 which should be the case of course in the comparison sample with the 

 pepsin. Next test 5 cc. portions of each mixture in the Esbach albumin- 

 ometer, adding the usual Esbach reagent (10 gm. picric acid and 20 gm. 

 citric acid with water to I liter). This reagent' precipitates albumoses 

 but not peptones, when used in excess, and from the extent of the reac- 

 tion in the tube some conclusion can be drawn as to degree of digestion. 

 A similar test should be made with potassium ferrocyanide and acetic acid 

 in place of the picric and citric acids. Ferrocyanhydric acid does not pre- 

 cipitate peptones. 



In another general method the action on solid coagulated protein is 

 observed. White of egg is drawn up into narrow glass tubes having an 

 internal diameter of about 2 mm. and coagulated by heat. The tubes are 

 then cut into lengths of I centimeter, thus exposing the ends of the coagu- 

 lated columns of albumin. These prepared tubes are then immersed in 

 the filtered gastric juice and in standard pepsin solution to be compared 

 and kept at a temperature of 40 some hours. The change in length of the 

 albumin column is taken as the measure of the peptic activity. The fil- 

 tered gastric juice must be largely diluted with water before making the 

 test, as salts and carbohydrates present interfere with the normal solution 

 of the end of the coagulated mass. The amount of albumin dissolved un- 

 der these conditions is said to be proportional to the square root of the 

 ferment strength, but the rule is far from exact. 



It has been explained above that according to late researches 

 pepsin and rennin are believed by many chemists to be identi- 

 cal substances. As the milk coagulating behavior seems to be 



