Crap, 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 (75 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 Dionza. 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 several 
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 
* Aga 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 affected after two days. 
acid of the same strength; and 
