Chap. VI. DIGESTION. 97 



coloured, viscid, slightly acid fluid was thus obtained. 

 The third lot was well soaked in a few drops of 

 glycerine, which is well known to dissolve pepsin. 

 Cubes of albumen (^^g- of an inch) were now placed 

 in the three fluids in watch-glasses, some of which 

 were kept for several days at about 90° Fahr. 

 ( 32°-2 Cent.), and others at the temperature of my 

 room; but none of the cubes were dissolved, the 

 angles remaining as sharp as ever. This fact pro- 

 bably indicates that the ferment is not secreted until 

 the glands are excited by the absorption of a minute 

 quantity of already soluble animal matter, — a con- 

 clusion which is supported by what we shall hereafter 

 see with respect to Dionaea. Dr. Hooker likewise found 

 that, although the fluid within the pitchers of Ne- 

 penthes possesses extraordinary power of digestion, yet 

 when removed from the' pitchers before they have 

 been excited and placed in a vessel, it has no such 

 power, although it is already acid; and we can 

 account for this fact only on the supposition that the 

 proper ferment is not secreted until some exciting 

 matter is absorbed. 



On three other occasions eight leaves were strongly 

 excited with albumen moistened with saliva; they 

 were then cut off, and allowed to soak for severaJ 

 hours or for a whole day in a few drops of glycerine. 

 Some of this extract was added to a little hydro- 

 chloric acid of various strengths (generally one to 

 400 of water), and minute cubes of albumen were 

 placed in the mixture.* In two of these trials the 

 cubes were not in the* least acted on ; but in the third 



* As a control experiment bits the albumen, as might have been 



of albumen were placed in the expected, was not in the least 



same glycerine with hydrochloric aflected after two days. 

 acid of the same strength; and 



