OF INSECTIVOROUS PLANTS 443 



When the liquor from non-stimulated pitchers was studied, it was 

 used as soon as possible after the opening of the pitcher. 



When liquor from stimulated pitchers was desired, recourse was had 

 to mechanical stimulation by chemically inert substances. In some 

 experiments, the glands of the pitcher were stroked repeatedly with a 

 camel's hair brush, and the cotton plug was then inserted; the liquor 

 was removed for study on the following day. In other experiments, 

 several small, round, solid glass beads, such as are used in fractionating 

 columns, were inserted into the newly opened pitcher; the cotton plug 

 was introduced; and the pitcher and its contents were shaken thoroughly 

 at intervals during one or more days, taking care not to wet the cotton 

 and thereby lose liquor; the liquor was finally removed for study. 



In all the tests for the presence of a protease, a bactericide was used 

 in order to exclude completely the action of micro-organisms. In some 

 experiments, sufficient sohd sodium fluoride was added to the mixture 

 of pitcher liquor and substrate to render the final concentration of the 

 fluoride 1 percent. In other experiments, a sufficient volume of a con- 

 centrated (2 percent.) aqueous solution of trikresol was added to render 

 the final concentration of that bactericide 0.2 percent. This concen- 

 tration of trikresol was found satisfactory by Graves and Kober (19) 

 in certain of their experiments with proteases. When the mixture of 

 pitcher liquor and substrate was diluted to a definite volume, the con- 

 centrated trikresol solution was added before the dilution to the final 

 volume was made. 



In each experiment, a blank or control determination was carried 

 out, using pitcher liquor which had previously been boiled, then permitted 

 to cool to the temperature of the room; the control was made in exactly 

 the same manner, in all other respects, as the determination proper. 

 The control or blank was always compared with the determination 

 proper, and due allowance was thus made for the possible action of any 

 thermostable catalyst present in the pitcher liquor, and also for any 

 action of the reagents on each other. 



The following reactions for the detection of a protease were used: — 



(1) The formol-titration of Sorensen. 



(2) The digestion of: — 



(a) carmine fibrin, 



(b) edestan, 



(c) protean derived from castor bean globulin, 



(d) ricin (Jacoby). 



