Cellulose.—­I did not obtain this substance in a separate state, but tried angular bits of dry wood, cork, sphagnum moss, linen, and cotton thread.  None of these bodies were in the least attacked by the secretion, and they caused only that moderate amount of inflection which is common to all inorganic objects.  Gun-cotton, which consists of cellulose, with the hydrogen replaced by nitrogen, was tried with the same result.  We have seen that a decoction of cabbage-leaves excites the most powerful inflection.  I therefore placed two little square bits of the blade of a cabbage-leaf, and four little cubes cut from the midrib, on six leaves of Drosera.  These became well inflected in 12 hrs., and remained so for between two and four days; the bits of cabbage being bathed all the time by acid secretion.  This shows that some exciting matter, to which I shall presently refer, had been absorbed; but the angles of the squares and cubes remained as sharp as ever, proving that the framework of cellulose had not been attacked.  Small square bits of spinach-leaves were tried with the same result; the glands pouring forth a moderate supply of acid secretion, and the tentacles remaining inflected for three days.  We have also seen that the delicate coats of pollen grains are not dissolved by the secretion.  It is well known that the gastric juice of animals does not attack cellulose.

Chlorophyll.—­This substance was tried, as it contains nitrogen.  Dr. Moore sent me some preserved in alcohol; it was dried, but soon deliquesced.  Particles were placed on four leaves; after 3 hrs. the secretion was acid; after 8 hrs. there was a good deal of inflection, which in 24 hrs. became fairly well marked.  After four days two of the leaves began to open, and the other two were then almost fully re-expanded.  It is therefore clear that this chlorophyll contained matter which excited the leaves to a moderate degree; but judging by the eye, little or none was dissolved; so that in a pure state it would not probably have been attacked by the secretion.  Dr. Sanderson tried that which I [page 126] used, as well as some freshly prepared, with artificial digestive liquid, and found that it was not digested.  Dr. Lauder Brunton likewise tried some prepared by the process given in the British Pharmacopoeia, and exposed it for five days at the temperature of 37o Cent. to digestive liquid, but it was not diminished in bulk, though the fluid acquired a slightly brown colour.  It was also tried with the glycerine extract of pancreas with a negative result.  Nor does chlorophyll seem affected by the intestinal secretions of various animals, judging by the colour of their excrement.