124 DROSEEA llOTUNDIFOLIA. Chap. VI. 



pepsin, but absorbs from it some aUmminous 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 

 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- 

 mi uim drops of a solution of one part to 437 of water were 

 l.laced on the discs of four leaves, each drop contaming the 

 quantity usually employed by me, namely g^o of a grain, or 

 •0u7-i 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 

 l)ure, for when four leaves were immersed in 2 dr. (I'l ml.) of 

 tJie 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 im- 

 mersion in pure water. That the urea, which was not per- 

 fectly 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 Brunt on informs 

 me that from experiments made at my request at St. Bartho- 

 lomew'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 deUcate wing and of the elytron of a Staphylinus 



