Cuar. VI. DIGESTION. 81 
dissolved, the angles remaining as sharp as ever. This fact 
probably 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 conclusion which is sup- 
ported by what we shall hereafter see with respect to Dionwa. 
Dr. Hooker likewise found that, although the fluid within 
the pitchers of Nepenthes 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.* 
* (With regard to Drosera Messrs. 
Rees and Will ¢* Bot. Zeitung,’ 1875, 
p. 715) state that a glycerine extract 
of Drosera leaves in a state of unex- 
cited secretion, and fairly free from 
insects, had no digestive action. But 
that the same extract, artificially acid- 
ulated, digested fibrin thoroughly 
well. 
The authors believe that the natu- 
ral acid of the glands was possibly 
destroyed in the process of preparing 
the extract. No conclusion can there- 
fore be drawn from their results as 
to the acidity of unexcited leaves. It 
is probable, however, judging from 
Von Gorup’s work on Nepenthes, that 
Drosera does not secrete the requisite 
amount of acid until it has been 
stimulated by the capture of insects. 
Rees and Will’s experiments are not 
quite conclusive on this point, but 
they tend to show that what is want- 
ing in the secretion of unescited leaves 
is the acid, not the ferment. The ex- 
periments of Von Gorup and Will on 
Nepenthes, as given in the ‘ Bot. Zei- 
tung,’ 1876, p. 473, do not confirm 
Hooker’s results on Nepenthes. The 
authors state that the secretion col- 
lected from pitchers which are free 
from insects is neutral, while the 
fluid of pitchers which contain the 
remains of insects is distinctly acid. 
‘The neutral secretion of the unexcited 
pitchers has no digestive power until 
it is acidulated, when it rapidly dis- 
solves fibrin. 
It seems, therefore, that the analogy 
with animal digestion pointed out at 
p- 106 does not altogether hold good. 
For Schiff states that in the gastric 
juice produced by mechanical irrita- 
tion, the element absent is the fer- 
ment, not the acid. 
On the other hand an interesting 
point of resemblance of a different 
kind has been made out by Vines in 
his paper on the digestive ferment of 
Nepenthes (‘Journal of the Linn. 
Soc.’ vol, xv. p. 427 ; also ‘Journal of 
Anatomy and Physiology,’ series ii. 
vol. xi. p. 124). 
The work was undertaken inde- 
pendently of Von Gorup and carried 
out by a different method, namely 
the preparation of a glycerine extract. 
Vines having found that the extract 
was far less active than the natural 
secretion used by Von Gorup, was 
led to an interesting explanation of 
this fact by Ebstein and Griitzner’s 
work on animal digestion. These 
writers show that the glycerine ex- 
tract gains in digestive activity if it 
is prepared from mucous membrane 
previously treated with acid. Vines 
accordingly treated Nepenthes witn 
one per cent acetic acid for 24 hrs. 
previously to the preparation of the 
extract, and thus obtained glycerine 
of much greater peptic activity. This 
G 
