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 case 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 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.

* Mucus from the air-passages is said in Marshall, ’Outlines of Physiology,’ vol. ii. 1867, p. 364, to contain some albumen.

Mller’s ‘Elements of Physiology,’ Eng.  Trans. vol. i., p. 514. [page 81]

from the time when the drops were placed on the leaves, all four had almost re-expanded.  They were then given little bits of meat, and these acted more powerfully than the solution.  One part of isinglass was next dissolved in 437 of water; the fluid thus formed was so thin that it could not be distinguished from pure water.  The usual-sized drops were placed on seven leaves, each of which thus received 1/960 of a grain (.0295 mg.).  Three of them were observed for 41 hrs., but were in no way affected; the fourth and fifth had two or three of their exterior tentacles inflected after 18 hrs.; the sixth had a few more; and the seventh had in addition the edge of the leaf just perceptibly curved inwards.  The tentacles of the four latter leaves began to re-expand after an additional interval of only 8 hrs.  Hence the 1/960 of a grain of isinglass is sufficient to affect very slightly the more sensitive or active leaves.  On one of the leaves, which had not been acted on by the weak solution, and on another, which had only two of its tentacles inflected, drops of the solution as thick as milk were placed; and next morning, after an interval of 16 hrs., both were found with all their tentacles strongly inflected.]