Page:Insectivorous Plants, Darwin, 1899.djvu/87

 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 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 inwards 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.

Saliva.―Human saliva, when evaporated, yields from 1.14 to 1.19 per cent, of residue; and this yields 0.25 per cent, of ashes, so that the proportion of nitrogenous matter which saliva contains must be small. Nevertheless, drops placed on the discs of eight leaves acted on them all. In one ease all the exterior tentacles, excepting nine, were inflected in 19 hrs. 30 m. ; in another case a few became so in 2 hrs., and after 7 hrs. 30 m. all those situated near where the drop lay, as well as the blade, were acted on. Since making these trials, I have many scores of times just touched the glands with the handle of my scalpel wetted with saliva, to ascertain whether a leaf was in an active condition ; for this was shown in the course of a few minutes by the bending inwards of the tentacles. The edible nest of the Chinese swallow is formed of matter secreted by the salivary glands; two grains were added to one ounce of distilled water (one part to 218), which was boiled for several minutes, but did not dissolve the whole. The usual-sized drops were placed on three leaves, and these in 1 hr. 30 m. were well, and in 2 hrs. 15 m. closely, inflected.

Isinglass.―Drops of a solution about as thick as milk, and of a still thicker solution, were placed on eight leaves, and the tentacles of all became inflected. In one case the exterior tentacles were well curved in after 6 hrs. 30 m., and the blade of the leaf to a partial extent after 24 hrs. As saliva acted so efficiently, and yet contains so small a proportion of nitrogenous matter, I tried how small a quantity of isinglass would act. One part was dissolved in 218 parts of distilled water, and drops were placed on four leaves. After 5 hrs. two of these were considerably and two moderately inflected; after 22 hrs. the former were greatly and the latter much more inflected. In the course of 48 hrs. from the time when the drops were placed