Urea.—­It seemed to me an interesting inquiry whether this refuse of the living body, which contains much nitrogen, would, like so many other animal fluids and substances, be absorbed by the glands of Drosera and cause inflection.  Half-minim drops of a solution of one part to 437 of water were placed on the discs of four leaves, each drop containing the quantity usually employed by me, namely 1/960 of a grain, or .0674 mg.; but the leaves were hardly at all affected.  They were then tested with bits of meat, and soon became closely inflected.  I repeated the same experiment on four leaves with some fresh urea prepared by Dr. Moore; after two days there was no inflection; I then gave them another dose, but still there was no inflection.  These leaves were afterwards tested with similarly sized drops of an infusion of raw meat, and in 6 hrs. there was considerable inflection, which became excessive in 24 hrs.  But the urea apparently was not quite pure, for when four leaves were immersed in 2 dr. (7.1 ml.) of the solution, so that all the glands, instead of merely those on the disc, were enabled to absorb any small amount of impurity in solution, there was considerable inflection after 24 hrs., certainly more than would have followed from a similar immersion in pure water.  That the urea, which was not perfectly white, should have contained a sufficient quantity of albuminous matter, or of some salt of ammonia, to have caused the above effect, is far from surprising, for, as we shall see in the next chapter, astonishingly small doses of ammonia are highly efficient.  We may therefore conclude that urea itself is not exciting or nutritious to Drosera; nor is it modified by the secretion, so as to be rendered nutritious, for, had this been the case, all the leaves with drops on their discs assuredly would have been well inflected.  Dr. Lauder Brunton informs me that from experiments made at my request at St. Bartholomew’s Hospital it appears that urea is not acted on by artificial gastric juice, that is by pepsin with hydrochloric acid.

Chitine.—­The chitinous coats of insects naturally captured by the leaves do not appear in the least corroded.  Small square pieces of the delicate wing and of the elytron of a Staphylinus [page 125] were placed on some leaves, and after these had re-expanded, the pieces were carefully examined.  Their angles were as sharp as ever, and they did not differ in appearance from the other wing and elytron of the same insect which had been left in water.  The elytron, however, had evidently yielded some nutritious matter, for the leaf remained clasped over it for four days; whereas the leaves with bits of the true wing re-expanded on the second day.  Any one who will examine the excrement of insect-eating animals will see how powerless their gastric juice is on chitine.