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Show 122 DROSERA ROTUNDIFOLIA. CHAP. VI. To these may be added dissolve~ sugar and ?l~m, diluted alcohol, and vegetable infusions not ?Ontalning album en for none of these, as shown in the last chapter,' excite inflection. Now, ~t is a rem~rkable fact which affords additional and nnportant evidence, tha; the ferment of Drosera is closely si1nilar to or identical with pepsin, that none of these same substances are, as far as it is known, digested by tho gastric juice of animals, though some of them are acted on by the other secretions of the alimon tary canal. Nothing 1nore need be said about some of tho above enumerated substances, excepting that they were repeatedly tried on the leaves of Dros~ra, and wore not in the least affected by the secretion. .1:\..bout tho others it will be advisable to give my experiments. Fibro-elastic Tissue.-Vve have already seen that when little cubes of meat, &c., were placed on leaves, the muscles, areolar tissue and cartilage were completely dissolved, but the fibroelasti~ tissue, even the most delicate threads, were left without the least signs of having been attacked. And it is well known that this tissue cannot be digested by the gastric juice of animals.* Mucin.-As this substance contains about 7 per cent. of nitrogen, I expected that it would have excited the loaves greatly and been digested by the secretion, but in this I was mistaken. From what is stated in chemical works, it appears extremely doubtful whether mucin can be prepared as a pure principle. That which I used (prepared by Dr. Moore) was dry and hard. Particles moistened with water were placed on four leaves, but after two days there was only a trace of inflection in the immediately adjoining tentacles. These leaves were then tried with bits of meat, and all four soon became strongly inflected. Some of the dried mucin was then soaked in water for two days, and little cubes of the proper size were placed on three leaves. After four days the tentacles * See, for instance, Schiff, 'Phys. de la Digestion,' 1867, tom. ii. p. 38. CHAP. VI. DIGESTION. 123 round the margins of the discs were a little inflected, and the secretion collected on the disc was acid, but the exterior tentacles were not affected. One leaf began to re-expand on the fourth day, and all were fully re-expanded on the sixth. The glands which had been in contact with the mucin were a little darkened. We may therefore conclude that a small amount of some impurity of a moderately exciting nature had been absorbed. That the mucin employed by me did contain some soluble matter was proved by Dr. Sanderson, who on subjecting it to artificial gastric juice found that in 1 hr. some was dissolved, but only in the proportion of 23 to 100 of fibrin during the same time. The cubes, though perhaps rather softer than those left in water for the same time, retained their angles as sharp as ever. We may therefore infer that the mucin itself was not dissolved or digested. Nor is it digested by the gastric juice of living animals, and according to Schiff* it is a layer of this substance which protects the coats of the stomach from being corroded during digestion. Pepsin.-My experiments are hardly worth giving, as it is scarcely possible to prepare pepsin free from other albuminoids ; but I was curious to ascertain, as far as that was possible, whether the ferment of the secretion of Drosera would act on the ferment of the gastric juice of animals. I first used the common pepsin sold for medicinal purposes, and afterwards some which was much purer, prepared for me by Dr. Moore. Five leaves to which a considerable quantity of the former was given remained inflected for five days; four of them then died, apparently from too great stimulation. I then tried Dr. Moore's pepsin, making it into a paste with water, and placing such small particles on the discs of. five leaves that all would have been quickly dissolved bad it been meat or albumen. The leaves were soon inflected; two of them began to re-expand after only 20 brs., and the other three were almost completely re-expanded after 44 hrs. Some of the glands which bad been in contact with the particles of pepsin, or with the acid secretion surrounding them, were singularly pale, whereas others were singularly dark-coloured. Some of the secretion was scraped off and examined under a high power; and it abounded with granules undistinguishable from those of pepsin left in water for the same length of time. We may therefore infer, as highly probable (remembering what small quantities were given), that the ferment of Drosera does not act on or digest * 'Le9ons phys. de la Digestion,' 1867, tom. ii. p. 304:. |