100 DROSERA ROTUNDIFOLIA. (Cuar. VI. 
dissolved in an hour; but the dissolution by the secretion of even a 
Jess amount would account for its action on Drosera. The residue 
left by the artificial digestive fluid at first yielded nothing more to it 
during several succeeding days. 
Substances which are not Digested by the Secretion. 
All the substances hitherto mentioned cause prolonged 
inflection of the tentacles, and are either completely or at 
least partially dissolved by the secretion. But there are 
many other substances, some of them containing nitrogen, 
which are not in the least acted on by the secretion, and do 
not induce inflection for a longer time than do inorganic and 
insoluble objects. These unexciting and indigestible sub- 
stances are, as far as I have observed, epidermic productions 
(such as bits of human nails, balls of hair, the quills of 
feathers), fibro-elastic tissue, mucin, pepsin. urea, chitine, 
chlorophyll, cellulose, gun-cotton, fat, oil, and starch. 
To these may be added dissolved sugar and gum, diluted 
alcohol, and vegetable infusions not containing albumen, for 
none of these, as shown in the last chapter, excite inflection. 
Now, it is a remarkable fact, which affords additional and 
important evidence, that the ferment of Drosera is closely 
similar to or identical with pepsin, that none of these same 
substances are, as far as it is known, digested by the gastric 
juice of animals, though some of them are acted on by the 
other secretions of the alimentary canal. Nothing more 
need be said about some of the above enumerated substances, 
excepting that they were repeatedly tried on the leaves of 
Drosera, and were not in the least affected by the secretion. 
About the others it will be advisable to give my experi- 
ments. 
Fibro-elastic Tissue-—We have already seen that when little cubes 
of meat, &c., were placed on leaves, the muscles, areclar tissue, and 
cartilage was completely dissolved, but the fibro-elastic tissue, even 
the most delicate threads, were left without the least signs of having 
been attacked. And it is well known that this tissue cannot be 
digested by the gastric juice of animals.* 
Mucin.—As this substance contains about 7 per cent. of nitrogen, I 
expected that it would have excited the leaves greatly and been 
digested by the secretion, but in this I was mistaken. From what is 
* See, for instance, Schiff, ‘ Phys. de la Digestion,’ 1867, tom. ii. p. 38. 
