740 



pepsin more closely, because tlien Michaems' way of solving the 

 problem would appear lo be erroneous. I, therefore, made two sets 

 of experiments; in the first I watched the behaviour of pepsin in 

 the electric field as accurately as possible; in the second I tried to 

 study in a different way from Michaki.is the bearing of the H-ion- 

 concentration on the enzyinie action. 



Above all I wanted an adequate quantity of pure pepsin. According 

 lo Pekelharing this is best obtained from the pure gastric juice of 

 a dog, provided with a Pawi.ow fistula in the slomacli and in the 

 esophagus. Such a dog was at my disfiosal. It had been operated 

 upon by Prof. Lamkuis and produced 300 — 500 c.c, of gastric juice 

 after being given a fictitious nieal two or three times a week. 



The enzyme was prepared after Peke],hai{ing. The gastric juice 

 was dialyzed and subsequently centrifugalized. The precipitate obtained 

 was washed and dried (pepsin 1). The centrifuged fluid mixed with 

 its own volume of a saturated solution of ammonium-sulfate, yields 

 another precipitate that was filtered off, dialyzed, dissolved in hydro- 

 chloric acid of about 0.05 n. at 37°. and dialyzed again. The gi-eater 

 part of it is then thrown out of solution again (pepsin 2). By a 

 prolonged dialyzation of pepsin, precipitated by ammonium sulfate, 

 and by dissolving it in oxalic acid and dialyzing it again for a very 

 long time, I have succeeded in obtaining a chlorin-free pepsin. So 

 we know now that pure pepsin is free from phosphorus (Pekelharing) 

 and from chlorine as well, and that the amount of chlorine in common 

 pepsin is to be ascribed to hydrochloric acid, either held back or 

 combined or adsorbed. The chlorine-free pepsin (3) I employed for 

 a good many experiments; its activity was equal to that of the 

 chlorine-containing pepsin 1 or 2. 



First set. The heliaviour of pure jiepsin in the electi-ic field. 



In order to avoid as many disturbances in my expei'iments as 

 possible, I improved upon my previous method. First of all I raised 

 the capacity of the non-polarisable electrodes. I then placed the 

 whole apparatus in a thermostat at 25°, and finally, at least in the 

 conclusive largest set of tests, I raised the specific gravity of the 

 pepsin solution by an indifferent, neutral substance with no affinity 

 for acids, viz. cane-sugar. The increased specific gravity, which I 

 had also applied in similar experiments with ptyalin, precludes 

 convection-streams of the fiuids during the passage of the electric current. 

 By proceeding thus no manner of disturbance took place, although 

 the apparatus was an elaborate contrivance and consequently difficult 



