86 DROSERA ROTUNDIFOLIA. Cuap. VI. 
It may be well to premise for the sake of any reader 
who knows nothing about the digestion of albuminous 
compounds by animals that this is effected by means 
of a ferment, pepsin, together with weak hydrochloric 
acid, though almost any acid will serve. Yet neither 
pepsin nor an acid by itself has any such power.* 
We have seen that when the glands of the disc are 
excited by the contact of any object, especially of 
one containing nitrogenous matter, the outer ten- 
tacles and often the blade become inflected ; the leaf 
being thus converted into a temporary cup or sto- 
mach. At the same time the discal glands secrete 
more copiously, and the secretion becomes acid. 
Moreover, they transmit some influence to the glands 
of the exterior tentacles, causing them to pour forth 
@ more copious secretion, which also becomes acid or 
more acid than it was before. 
As this result is an important one, I will give the 
evidence. The secretion of many glands on thirty 
leaves, which had not been in any way excited, was 
tested with litnius paper ;. and the secretion of twenty- 
two of these leaves did not in the least affect the colour, 
whereas that of eight caused an exceedingly feeble 
and sometimes doubtful tinge of red. Two other 
old leaves, however, which appeared to have been in- 
flected several times, acted much more decidedly on 
the paper. Particles of clean glass were then placed 
on five of the leaves, cubes of albumen on six, and 
bits of raw meat on three, on none of which was the 
secretion at this time in the least acid. After an 
interval of 24 hrs., when almost all the tentacles on 
* It appears, however, accord- though slowly, a very minute 
ing to Schiff, and contrary to the quantity of coagulated albumen. 
opinion of some physiologists, Schiff, ‘Phys. de la Digestion,’ 
that weak hydrochloric dissolves, tom. il. 1867, p. 25 
