Quick inflection depends partly on the quantity of the substance given, so that many glands are simultaneously affected, partly on the facility with which it is penetrated and liquefied by the secretion, partly on its nature, but chiefly on the presence of exciting matter already in solution. Thus saliva, or a weak solution of raw meat, acts much more quickly than even a strong solution of gelatine. So again leaves which have re-expanded, after absorbing drops of a solution of pure gelatine or isinglass (the latter being the more powerful of the two), if given bits of meat, are inflected much more energetically and quickly than they were before, notwithstanding that some rest is generally requisite between two acts of inflection. We probably see the influence of texture in gelatine and globulin when softened by having been soaked in water acting more quickly than when merely wetted. It may be partly due to changed texture, and partly to changed chemical nature, that albumen, which had been kept for some time, and gluten which had been subjected to weak hydrochloric acid, act more quickly than these substances in their fresh state.
The length of time during which the tentacles remain inflected largely depends on the quantity of the substance given, partly on the facility with which it is penetrated or acted on by the secretion, and partly on its essential nature. The tentacles always remain inflected much longer over large bits or large drops than over small bits or drops. Texture probably plays a part in determining the extraordinary length of time during which the tentacles remain inflected [page 133] over the hard grains of chemically prepared casein. But the tentacles remain inflected for an equally long time over finely powdered, precipitated phosphate of lime; phosphorus in this latter case evidently being the attraction, and animal matter in the case of casein. The leaves remain long inflected over insects, but it is doubtful how far this is due to the protection afforded by their chitinous integuments; for animal matter is soon extracted from insects (probably by exosmose from their bodies into the dense surrounding secretion), as shown by the prompt inflection of the leaves. We see the influence of the nature of different substances in bits of meat, albumen, and fresh gluten acting very differently from equal-sized bits of gelatine, areolar tissue, and the fibrous basis of bone. The former cause not only far more prompt and energetic, but more prolonged, inflection than do the latter. Hence we are, I think, justified in believing that gelatine, areolar tissue, and the fibrous basis of bone, would be far less nutritious to Drosera than such substances as insects, meat, albumen, &c. This is an interesting conclusion, as it is known that gelatine affords but little nutriment to animals; and so, probably, would areolar tissue and the fibrous basis of bone. The chondrin which I used acted more powerfully than gelatine, but then I do not know that it was pure. It is a more remarkable fact that fibrin, which belongs to the great class of Proteids,* including albumen in one of its sub-groups, does not excite the tentacles in a greater degree, or keep them inflected for a longer time, than does gelatine, or
* See the classification adopted by Dr. Michael Foster in Watts' 'Dictionary of Chemistry,' Supplement 1872, page 969. [page 134]
areolar tissue, or the fibrous basis of bone. It is not known how long an animal would survive if fed on fibrin alone, but Dr. Sanderson has no doubt longer than on gelatine, and it would be hardly rash to predict, judging from the effects on Drosera, that albumen would be found more nutritious than fibrin. Globulin likewise belongs to the Proteids, forming another sub-group, and this substance, though containing some matter which excited Drosera rather strongly, was hardly attacked by the secretion, and was very little or very slowly attacked by gastric juice. How far globulin would be nutritious to animals is not known. We thus see how differently the above specified several digestible substances act on Drosera; and we may infer, as highly probable, that they would in like manner be nutritious in very different degrees both to Drosera and to animals.