We thus see that, excluding the experiments with water, sixty-one leaves were tried with drops of the [page 79] above-named non-nitrogenous fluids; and the tentacles were not in a single case inflected.

[With respect to nitrogenous fluids, the first which came to hand were tried.  The experiments were made at the same time and in exactly the same manner as the foregoing.  As it was immediately evident that these fluids produced a great effect, I neglected in most cases to record how soon the tentacles became inflected.  But this always occurred in less than 24 hrs.; whilst the drops of non-nitrogenous fluids which produced no effect were observed in every case during a considerably longer period.

Milk.—­Drops were placed on sixteen leaves, and the tentacles of all, as well as the blades of several, soon became greatly inflected.  The periods were recorded in only three cases, namely, with leaves on which unusually small drops had been placed.  Their tentacles were somewhat inflected in 45 m.; and after 7 hrs. 45 m. the blades of two were so much curved inwards that they formed little cups enclosing the drops.  These leaves re-expanded on the third day.  On another occasion the blade of a leaf was much inflected in 5 hrs. after a drop of milk had been placed on it.

Human Urine.—­Drops were placed on twelve leaves, and the tentacles of all, with a single exception, became greatly inflected.  Owing, I presume, to differences in the chemical nature of the urine on different occasions, the time required for the movements of the tentacles varied much, but was always effected in under 24 hrs.  In two instances I recorded that all the exterior tentacles were completely inflected in 17 hrs., but not the blade of the leaf.  In another case the edges of a leaf, after 25 hrs. 30 m., became so strongly inflected that it was converted into a cup.  The power of urine does not lie in the urea, which, as we shall hereafter see, is inoperative.

Albumen (fresh from a hen’s egg), placed on seven leaves, caused the tentacles of six of them to be well inflected.  In one case the edge of the leaf itself became much curled in after 20 hrs.  The one leaf which was unaffected remained so for 26 hrs., and was then treated with a drop of milk, and this caused the tentacles to bend inwards in 12 hrs.

Cold Filtered Infusion of Raw Meat.—­This was tried only on a single leaf, which had most of its outer tentacles and the blade inflected in 19 hrs.  During subsequent years, I repeatedly used this infusion to test leaves which had been experimented [page 80] on with other substances, and it was found to act most energetically, but as no exact account of these trials was kept, they are not here introduced.

Mucus.—­Thick and thin mucus from the bronchial tubes, placed on three leaves, caused inflection.  A leaf with thin mucus had its marginal tentacles and blade somewhat curved inward in 5 hrs. 30 m., and greatly so in 20 hrs.  The action of this fluid no doubt is due either to the saliva or to some albuminous matter* mingled with it, and not, as we shall see in the next chapter, to mucin or the chemical principle of mucus.