OF INSECTIVOROUS PLANTS 425 



dissolved in a considerably shorter time; after digestion for 2 hours, the 

 resulting solution gave a very sUght precipitate on neutralization, and 

 gave a biuret reaction as intense as that obtained in the case of 

 formic acid. 



The solutions, obtained by digestion, contained much more protein 

 (metaprotein) immediately after the fibrin had dissolved, than in later 

 stages of the digestion. This protein gradually vanished, and was dis- 

 placed by peptone as the period of digestion lengthened. From these 

 phenomena, which were repeatedly obser\^ed, it followed that, apparent- 

 ly, peptone represented the second and not the first stage of the action 

 of the enzyme. 



Von Gorup and Will, who made the necessary control experiments 

 on their reagents, do not hesitate distinctly to designate the acid liquor 

 of the stimulated Nepenthes pitchers as a solution of plant pepsin. The 

 neutral secretion of the non-stimulated pitcher, like pepsin in the absence 

 of free acid, exerts no digestive action. 



Vines (5) dehydrated pitchers of Nepenthes species (iV. hybrida and 

 A'', gracilis) by means of absolute alcohol, converted their tissue into a 

 pulp, and extracted this with glycerol in order to obtain a solution of the 

 protease. As a substrate, he used fibrin which had been soaked in 0.2 

 percent hydrochloric acid until gelatinous. When the fibrin was in- 

 cubated at 40° C. with the enz>Tne solution to which a few drops of 0.2 

 percent hydrochloric acid had previously been added, at the end of 8 

 hours the substrate showed signs of digestion and, after filtration, the 

 solution gave a distinct peptone (biuret) reaction. Control experiments 

 on fibrin plus enz\TTie solution, and on fibrin plus 0.2 percent hydrochloric 

 acid, did not show digestion and did not give a biuret reaction. Hence 

 the glands of the pitchers contained a proteolytic enzyme, which was 

 soluble in glycerol and was active only in the presence of acid. 



Pitchers were gathered from the same plants (of the species mentioned 

 above) at the same time. Some pitchers were immediately treated as 

 outlined above for the preparation of a glycerol extract. Other pitchers 

 were first treated with dilute (1 percent) acetic acid for 24 hours, then 

 the glycerol extract was prepared, using the procedure already described. 

 In every set of experiments, the extract from the pitchers, which received 

 the preliminary treatment with acetic acid, was higher in proteolytic 

 power than the extract from pitchers not so treated. Thus the same 

 volume of each extract was permitted to act on a pellet of swollen fibrin 

 in the presence of 2 cc. of 0.2 percent hydrochloric acid at a temperature 

 of 40° C. The fibrin pellets were similar. At the end of 6 hours, the 



