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Show 132 DROSERA ROTUNDIFOLIA. CHAP . VI. rates and in very different degr~es; and t~e tentacles remain inflected for very different periods of tI.m e. Quick inflection depends partly on the quant .t f the substance given, so that many glands are sIi mYuol taneously affected, partly on t h e £a ci· rI ty ~I·t h which it is penetrated and liquefied by the secretion, partly on its nature, but chiefly on the prese~ce of exciting matter already in solution. Thus sah~a, 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 isingla.ss (t.he lat~er being the more powerful of the two), If ?Iven bits of meat are inflected much more energetically and quickly' than they were befo~e: notwithstanding that some rest is generally requisite between two acts of inflection. We probably see the influence of texture in gelatine and globulin ~hen softene~ 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 has been kept for some time, and gluten which has been subj ected to weak hydrochloric acid, act more quickly than these substances in their fresh state. The length of ti1ne 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 part~y 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 tjme during which the tentacles remain inflected CHAP. VI. DIGESTION. 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' ' Diet. of Chemistry,' Supplement 1872, p. 969. |