Small cubes of hard casein, moistened with water, were placed on two leaves; after three days one cube had its angles a little rounded, and after seven days both consisted of rounded softened masses, in the midst of much viscid and acid secretion; but it must not be inferred from this fact that the angles were dissolved, for cubes immersed in water were similarly acted on.  After nine days these leaves began to re-expand, but in this and other cases the casein did not appear, as far as could be judged by the eye, much, if at all, reduced in bulk.  According to Hoppe-Seyler and Lubavin* casein consists of an albuminous, with

* Dr. Lauder Brunton, ‘Handbook for Phys.  Lab.’ p. 529. [page 116]

a non-albuminous, substance; and the absorption of a very small quantity of the former would excite the leaves, and yet not decrease the casein to a perceptible degree.  Schiff asserts*—­and this is an important fact for us—­that “la casine purifie des chemistes est un corps presque compltement inattaquable par le suc gastrique.”  So that here we have another point of accordance between the secretion of Drosera and gastric juice, as both act so differently on the fresh casein of milk, and on that prepared by chemists.

A few trials were made with cheese; cubes of 1/20 of an inch (1.27 mm.) were placed on four leaves, and these after one or two days became well inflected, their glands pouring forth much acid secretion.  After five days they began to re-expand, but one died, and some of the glands on the other leaves were injured.  Judging by the eye, the softened and subsided masses of cheese, left on the discs, were very little or not at all reduced in bulk.  We may, however, infer from the time during which the tentacles remained inflected,—­from the changed colour of some of the glands,—­and from the injury done to others, that matter had been absorbed from the cheese.

Legumin.—­I did not procure this substance in a separate state; but there can hardly be a doubt that it would be easily digested, judging from the powerful effect produced by drops of a decoction of green peas, as described in the last chapter.  Thin slices of a dried pea, after being soaked in water, were placed on two leaves; these became somewhat inflected in the course of a single hour, and most strongly so in 21 hrs.  They re-expanded after three or four days.

* ‘Leons’ &c. tom. ii. page 153. [page 117]

The slices were not liquefied, for the walls of the cells, composed of cellulose, are not in the least acted on by the secretion.

Pollen.—­A little fresh pollen from the common pea was placed on the discs of five leaves, which soon became closely inflected, and remained so for two or three days.