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Show 124 DROSERA ROTUNDIFOLIA. CHAP. VI. · b t .absorbs from it some albuminous impurity which pepsin, u . . t't . , 1 . ·hl induces inflection, and whiCh In large quan I y IS ng y I·l lJ·U I'IO· US. Dr · Lauder . Brun. ton at my Teq· uest 'den deavlodu dre' d. to ascertain whether pepsm with h~drochl.oric aCI wou Igcst · and as far as he could Judge, It had no such power. pGeapsstmric, juice", therefore, apparently agrees I· n tln ·s re·s pec t WI' th the secretion of Drosera. . . . . un?:.e a. -It seemed to me an interestmg I.n quiry w]h eth·te r this refuse of the living body, which contams muc 1 ni ·rogen, ould like so many other animal fluids and substances, be ~:vbsorbed by the glands of Drosera and cause inflection. Halfminim drops of a solution of one pai't to 437 of wat~r were placed on the discs of four leaves, each drop contmnwg tho quantity usually employed by me, namely 0} 0 of a grain, or ·0674 mg.; but the leaves were hardly at all affected. They were then tested with bits of meat, and soon bocarno closely inflected. I repeated the same experiment on four loaves with some fresh urea prepared by Dr. Moore; after two days there was no inflection; I then gave them another close, but still there was no inflection. These leaves were aftenmrds tested with similarly sized drops of an infusion of Taw meat, and in 6 hrs. there was considerable inflection, which became excessive in 24 hrs. But the urea appaTently was not quite pure, for when four leaves were im~ erscd in ~ dr. (7·1 ml.) of the solution, so that all the glands, Instoacl of merely those on the disc, were enabled to absorb any small amount of iu1pnrity in solution, there was considerable inflection after 21 hrs., certainly more than would have followed from a similar immersion in pure water. That the urea, which wu,s 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 do. es of ammonia are highly efficient. We may therefore conclude that urea Hsolf is not exciting or nutritious to D1·o era; nor is it mo<lified by the secretion, so as to be rendered nutritious, for, lutd 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 CHAP. VI. DIGES'l'ION. 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 wbjch had been left in water. The elytron, however, 1md evidently yielded some nutritious matter, for the leaf Temained 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 chi tine. Cellulose.-! djd 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 reFmlt. vVe have seen that a decoction of cabbage-leaves excites the most powerful inflection. I theTefore pJaced 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 t-ried with the same result; the glands pouring forth a moderate supply of acid secretion, and the tentacles remaining infhcted for three days. We have also seen that the delicate coat~ of pollen grains are not dissolved by the secretion. It is well known that the gastric juice of animals does not attack cellulose. Uhlor·ophyll.-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 hi's. 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 |