102 DROSERA ROTUxNDIFOLIA. [Chap. VI. 



ly dark-coloured. Some of the Becrction was scraped off and ex- 

 amined under a high power; and it abounded with granules undis- 

 tinguishable from those of pepsin left in water for the same length 

 of time. VVc may therefore infer, as highly probable (remembering 

 what small quantities were given), that the ferment of Drosera 

 does not act on or digest pepsin, but absorbs from it some albu- 

 minous impurity which induces inflection, and which in large 

 quantity is highly injurious. Dr. Lauder Brunton at my request 

 endeavoured to ascertain whether pepsin with hydrochloric acid 

 would digest pepsin, and as far as he could judge, it had no such 

 power. Gastric juice, therefore, apparently agrees in this respect 

 with the secretion of Drosera. 



Urea. It seemed to me an interesting inquiry whether this re- 

 fuse 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. Hnlf-minim drops of a solu- 

 tion 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 ^^^ of a grain, or .0074 mg.; but the leaves were hardly at 

 all afTected. They were then tested with bits of meat, and soon be- 

 came 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 c.c.) 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 alx)ve 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 the urea itself is not 

 exciting or nutritious to Drosera; nor is it modified by the secre- 

 tion, 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. liartholomew'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 were placed 

 on some leaves, and after these had re-expanded, the pieces were 

 carefully examine<l. 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 Inrn left in water. The elytron, however. 



