I believe that the explanation lies simply in the fact that gluten is too powerful a stimulant (like raw meat, or phosphate of lime, or even too large a piece of albumen), and that it injures or kills the glands before they have had time to pour forth a sufficient supply of the proper secretion. That some matter is absorbed from the gluten, we have clear evidence in the length of time during which the tentacles remain inflected, and in the greatly changed colour of the glands.

At the suggestion of Dr. Sanderson, some gluten was left for 15 hrs. in weak hydrochloric acid (.02 per cent.), in order to remove the starch. It became colourless, more transparent, and swollen. Small portions were washed and placed on five leaves, which were soon closely inflected, but to my surprise re-expanded completely in 48 hrs. A mere vestige of gluten was left on two of the leaves, and not a vestige on the other three. The viscid and acid secretion, which remained on the discs of the three latter leaves, was scraped off and examined by my son under a high power; but nothing could be seen except a little dirt, and a good many starch grains which had not been dissolved by the hydrochloric acid. Some of the glands were rather pale. We thus learn that gluten, treated with weak hydrochloric acid, is not so powerful or so enduring a [page 120] stimulant as fresh gluten, and does not much injure the glands; and we further learn that it can be digested quickly and completely by the secretion.

[Globulin or Crystallin.--This substance was kindly prepared for me from the lens of the eye by Dr. Moore, and consisted of hard, colourless, transparent fragments. It is said* that globulin ought to "swell up in water and dissolve, for the most part forming a gummy liquid;" but this did not occur with the above fragments, though kept in water for four days. Particles, some moistened with water, others with weak hydrochloric acid, others soaked in water for one or two days, were placed on nineteen leaves. Most of these leaves, especially those with the long soaked particles, became strongly inflected in a few hours. The greater number re-expanded after three or four days; but three of the leaves remained inflected during one, two, or three additional days. Hence some exciting matter must have been absorbed; but the fragments, though perhaps softened in a greater degree than those kept for the same time in water, retained all their angles as sharp as ever. As globulin is an albuminous substance, I was astonished at this result; and my object being to compare the action of the secretion with that of gastric juice, I asked Dr. Burdon Sanderson to try some of the globulin used by me. He reports that "it was subjected to a liquid containing 0.2 per cent. of hydrochloric acid, and about 1 per cent. of glycerine extract of the stomach of a dog. It was then ascertained that this liquid was capable of digesting 1.31 of its weight of unboiled fibrin in 1 hr.; whereas, during the hour, only 0.141 of the above globulin was dissolved. In both cases an excess of the substance to be digested was subjected to the liquid." We thus see that within the same time less than one-ninth by weight of globulin than of fibrin was dissolved; and bearing in mind that pepsin with acids of the acetic series has only about one-third of the digestive power of pepsin with hydrochloric acid, it is not surprising that the fragments of

* Watts' 'Dictionary of Chemistry,' vol. ii. page 874.

I may add that Dr. Sanderson prepared some fresh globulin by Schmidt's method, and of this 0.865 was dissolved within the same time, namely, one hour; so that it was far more soluble than that which I used, though less soluble than fibrin, of which, as we have seen, 1.31 was dissolved. I wish that I had tried on Drosera globulin prepared by this method. [page 121]

globulin were not corroded or rounded by the secretion of Drosera, though some soluble matter was certainly extracted from them and absorbed by the glands.

Haematin.--Some dark red granules, prepared from bullock's blood, were given me; these were found by Dr.

Charles Darwin

All Pages of This Book