DEFENSIVE FERMENTS 247 



a similar range of activity, and (c) an ereptase active in both acid and 

 alkaline media and capable of splitting partially hydrolized proteins into 

 amino-acids. Of these ferments only the ereptase is able to act in the 

 presence of blood serum and tissue fluids because the others are inhibited 

 by the activity of antiferment constantly present. The serum protease 

 is a polyvalent trypsin-like ferment active in neutral, in slightly acid, 

 or in slightly alkaline media; it is completely inhibited by the antifer- 

 ment of the circulating fluid. It becomes active only when the anti- 

 ferment is removed and is capable of digesting native protein to the 

 amino-acid stage. It is present in fairly large amounts in sera of the 

 lower animals, but is found in only small quantities in human serum. 

 The serum peptidase is a polyvalent ferment which operates in the 

 same type of media as the protease ; it is present in normal human serum 

 in small amounts, is not inhibited by antiferment and digests partly 

 hydrolized proteins to the amino-acid stage. Since the toxic fractions 

 of proteins are principally in the form of proteoses and pepton, the 

 peptidase apparently is the most important ferment in destroying such 

 toxic bodies. 



The importance of esterases in the blood is not at all clear. It is 

 known that lymphocytes contain a lipase, and it has been suggested 

 that the accumulation of these cells about tuberculous foci may indicate 

 the importance of this ferment in breaking down the waxy capsule of 

 the bacilli. Jobling, Petersen and Eggstein recommend the following 

 methods for the determination of serum protease and serum esterase 

 (Journal of Experimental Medicine, vol. xxii.). 



" The technic for proteases is as follows : The clear hemoglobin- free serum 

 is measured with an accurate i.o c.c. pipette into a rather wide test-tube (about 

 18 mm.). To the tube 0.5 to 0.75 c.c. of chloroform is added and the tube is 

 sharply shaken, at intervals, until a milky emulsion is formed. We prefer chloro- 

 form because the 'emulsion is more stable than with ether or other lipoid solvents. 

 A control tube is inactivated at 60 C. for thirty minutes and a drop of toluol is 

 then added in place of chloroform. Both tubes are then incubated over night 

 (fifteen to sixteen hours at 37). In the morning about i.o c.c. of a mixture 

 of 10 per cent, acetic acid plus 20 per cent, salt solution is added, and the tubes 

 are then gently warmed in a water bath until the chloroform has been evaporated. 

 About 2 or 3 c.c. of distilled water are then added slowly and the tubes boiled 

 for at least ten minutes. The coagulated protein is filtered off by means of 

 hard filter paper, previously moistened, the filtrate being permitted to ^ filter 

 directly into the large tubes used for oxidizing. The tubes are then oxidized 

 and Nesslerized according to the usual Folin method, the readings being made 

 against varying dilutions of the i mg. standard, so that test readings are made 

 against standard of apparently equal color." 



" Serum esterase has been determined as follows : To i.o c.c. of the serum, 

 i.o c.c. of neutral, redistilled ethyl butyrate and 0.5 c.c. toluol are added, the 

 volume being brought to 10.0 c.c. with physiological salt solution. The flasks 

 are then shaken 100 times and incubated for four hours ; 25 c.c. of neutral 95 per 

 cent, alcohol are then added to each flask and the acidity which has developed is 

 titrated with N/5O sodium hydrate (alcoholic) to a faint pink with phenolphtha- 

 lein. After deducting the proper controls, i.e., serum alone, ethyl butyrate alone, 

 etc., the esterase index is expressed in terms of c.c. of N/ioo sodium hydrate used to 

 neutralize the acidity developed by i.o c.c. of serum from i.o c.c. of ethyl butyrate." 



Ferment-Antiferment Balance. The activity of various ferments 

 in the body is probably effective in various degrees at all times, and 

 this activity probably plays a certain part in normal metabolism. Cer- 



