[Fibro-elastic Tissue.—We 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 fibro-elastic 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 leaves 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. [page 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.