Chap. VI.J DIGESTION. 101 



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 nitro- 

 gen, 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 mois- 

 tened 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 

 round the margins of the discs were a little inflected, and the secre- 

 tion 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 artiflcial gastric juice found 

 that in 1 hr. some was dissolved, but only in the proportion of 23 

 to 100 of fibrin during the same tijne. 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 beinqr 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 had it been meat or albumen. 

 The leaves were soon inflected; two of them began to re-expand 

 after only 20 hrs., and the other three were almost completely re- 

 expanded' after 44 hrs. Some of the glands which had been in con- 

 tact with the particles of pepsin, or with the aci<l secretion sur- 

 rounding them, were singularly pale, whereas others were singular- 



** 8re, tor Instance. Schlff. " * Lecons phys. de la Dlge- 



' Phvs. de la Digestion,' 1867, tlon,' 1867, torn. 11. p. 304. 

 torn. II. p. 38. 



