Cuar. XVI. SECRETION, ABSORPTION, DIGESTION. 389 
see that objects not containing soluble matter have 
little or no power of exciting the glands to secrete 
Non-nitrogenous fluids, if dense, cause the glands to 
pour forth a large supply of viscid fluid, but this is 
not in the least acid. On the other hand, the secre- 
tion from glands excited by contact with nitrogenous 
solids or liquids is invariably acid, and is so copious 
that it often runs down the leaves and collects 
within the naturally incurved margins. The secre- 
tion in this state has the power of quickly dissolving, 
that is of digesting, the muscles of insects, meat, 
cartilage, albumen, fibrin, gelatine, and casein as 
it exists in the curds of milk. The glands are 
strongly excited by chemically prepared casein and 
gluten; but these substances (the latter not having 
been soaked in weak hydrochloric acid) are only 
partially dissolved, as was likewise the case with 
Drosera. The secretion, when containing animal 
matter in solution, whether derived from solids 
or from liquids, such as an infusion of raw meat, 
milk, or a weak solution of carbonate of ammonia, 
is quickly absorbed; and the glands, which were 
before limpid and of a greenish colour, become brownish 
and contain masses of aggregated granular matter. 
This matter, from its spontaneous movements, no doubt 
consists of protoplasm. No such effect is produced 
by the action of non-nitrogenous fluids. After the 
glands have been excited to secrete freely, they cease 
for a time to secrete, but begin again in the course of 
a few days. 
Glands in contact with pollen, the leaves of other 
plants, and various kinds of seeds, pour forth much 
acid secretion, and afterwards absorb matter probably 
of an albuminoug nature from them. Nor can the 
benefit thus derived be insignificant, for a considerable 
