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Show 92 DROSERA ROTUNDIFOLIA. CHAP. VI. I -'11 w give in detail my experiments on the Wl no d' ·a· digestive power of the secretion of. Drosera, 1v1 1ng the substances tried into two senes, namely those which are digested more or less completely, and those whw. h are not digested. We shall presently s.ee. t.ha t all these substances are acted on by the gastnc JUICe of the higher animals in the same. manner. I beg leave to call attention to the expenments under the head albumen showing that the secretion loses its power when ~eutralised by an alkali, and r cov rs it when an acid is added. S~tbstances which are C01npletely Or partially digested by the Secretion of Drosera. Albu1nen.-After having tried various substances, Dr. Burdon Sanderson suggested to me the use of cubes of coagulated albumen or hard-boiled egg. I 1nay preInise that five cubes of the same size as those used in the following experiments were placed for th sake of comparison at the same time on wet moss close to the plants of Drosera. The weather was hot, and ·after four days some of the cubes were discoloured and mouldy, with their angles a little rounded; but they were not surrounded by a zone of transparent fluid as in the case of those undergoing dig stion. Oth r cubes retained their angles and white colour. After eight days all were somewhat reduced in size, discoloured, with their angles much rounded. N ev rtheless in four out of the five specimens, the central parts were still white !ind opaque. So that their state diffi red widely, as we shall see, from that of the cubes subjected to the action of the secretion. Expe1·iment l. -Rather large cubes of albumen were first tried ; the tentacles were well inflected in 24 hrs. ; after an CHAP. VI. DIGES'.CION. 93 additional day the angles of the cubes were dissolved and rounded;* but the cubes were too large, so that the leaves were injured, and after seven days one died and the others were dying. Albumen which has been kept for four or five days, and which, it may be presumed, has begun to decay slightly, seems to act more quickly than freshly boiled eggs. As the latter were generally used, I often moistened them with a little saliva, to make the tentacles close more quickly. Ex,,eriment 2.-A cube of fo of an inch (i.e. with each side 11>- of an inch, or 2·54 mm., in length) was placed on a leaf, and after 50 hrs. it was converted into a sphere about lo of an inch (1·905 mm.) in diameter, surrounded by perfectly transparent fluid. After ten days the leaf re-expanded, but there was still left on the disc a minute bit of albumen now rendered transparent. More albumen had been given to this leaf than could be dissolved or digested. Experiment 3.-Two cubes of albumen of 2~ of an inch (1·27 mm.) were placed on two leaves. After 46 hrs. every atom of one was dissolved, and most of the liquefied matter was absorbed, the fluid which remained being in this, as in all other cases, very acid and viscid. The other cube was acted on at a rather slower rate. Experiment 4.-Two cubes of albumen of the same size as the last were placed on two leaves, and were converted in 50 hrs. into two large drops of transparent fluid; but when these were removed from beneath the inflected tentacles, and viewed by reflected light under the microscope, fine streaks of white opaque matter could be seen in the one, and traces of similar streaks in the other. The drops were replaced on the leaves, which re-expanded after 10 days; and now nothing was left except a very little transparent acid fluid. Experiment 5.-This experiment was sljghtly varied, so that the albumen might he more quickly exposed to the action of the secretion. Two cubes, each of about to of an inch ( · 635 mm.), were placed on the same leaf, and two similar cubes on another * In all my numerous experiments on the digestion of cubes of albumen, the angles and edges were invariably first rounded. Now, Schiff states ( 'Le<;ons phys. de la Digestion,' vol. ii. 186 7, p. 14~) that this is charac-toristic of the digestion of albumen by the gastric juice of animals. On the other hand, he 1·ernarks, "les dissolutions, en rhimie, ont lieu sur toute la surface des corps en contact avec l'agen,t dissolvant." |