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Show 86· DROSERA RO'rUNDIFOLIA. CHAP. VI. It may be well to pre1nise fo1~ the .sake of any r~ader who knows nothing about the d1gest1on of albuminous compounds by animals that this. is effected by mea~s of a ferment, pepsin, together with weak hydrochlonc acid, though almost any acid will serve. Yet neither pepsin nor an acid by itself has any such power.* We have seen that when the gland.s of the disc are excited by the contact of any object, especially of one containing nitrogenous matter, the outer tentacles and often the blade become inflected ; the leaf being thus converted into a temporary cup or stoInach. At the same tin1e the discal glands secrete more copiously, and the secretion becomes acid. Moreover, they transmit some influence to the glands of the exterior tentacles, causing them to pour forth a more copious secretion, which also bee mes acid or more acid than it was before. As this result is an important one, I will give the evidence. The secretion of many glands on thirty leaves, which had not been in any way excited, was tested with lit1nus paper ; and the secretion of twentytwo of these leaves did not in the least affect the colour, whereas that of eight caused an exceedingly feeble and sometimes doubtful tinge of red. Two other old leaves, however, which appeared to have been inflected several times, acted much more decidedly on the paper. Particles of clean glass were then placed on five of the leaves, cubes of albumen on six, and bits of raw meat on three, on none of which was the secretion at this time in the least acid. After an interval of 24 hrs., when almost all the tentacles on * It appears, however, accordin~ ~o Schiff, and contrary to the opmwn of some physiologbts that weak hydrochloric dissolves: though slowly, o. very minuto quantity of coagulated albumen. Schiff, 'Pbys. de la Digestion,' tom. ii. 1867, p. 25. CHAP. VI. DIGESTION. 87 these fourteen leaves had become more or less inflected, I again tested the secretion, selecting glands which had not as yet reached the centre or touched any object, and it was now plainly acid. The degree of acidity of the secretion varied somewhat on the glands of the same leaf. On some leaves, a few tentacles did not, from some unknown cause, become inflected, as often happens ; and in five instances their secretion was found not to be in the least acid · whilst the secretion of the adjoining and inflected' tentacles on the same leaf was decidedly acid. With leaves excited by particles of glass placed on the central glands, the secretion which collects on the disc beneath them was much more strongly acid than that poured forth from the exterior tentacles, which were as yet only moderately inflected. When bits of albumen (and this is naturally alkaline), or bits of meat were placed on the disc, the secretion collected beneath them was likewise strongly acid. As raw meat moistened with water is slightly acid, I compared its action on litmus paper before it was placed on the leaves, and afterwards when bathed ·in the secretion ; and there could not be the least doubt that the latter was very much more acid. I have indeed tried hundreds of times the state of the secretion on the discs of leaves which were inflected over various objects, and never failed to find it acid. We may, therefore, conclude that the secretion from unexcited leaves, though extreme I y viscid, is not acid or only slightly so, but that it becomes acid, or much more strongly so, after the tentacles have begun to bend over any inorganic or organic object; and still more strongly acid after the tentacles have remained for some time closely clasped over any object. I may here remi~d the reader that the secretion |