It must not be supposed from these facts that the grains of chlorophyll, as they exist in living plants, cannot be attacked by the secretion; for these grains consist of protoplasm merely coloured by chlorophyll.  My son Francis placed a thin slice of spinach leaf, moistened with saliva, on a leaf of Drosera, and other slices on damp cotton-wool, all exposed to the same temperature.  After 19 hrs. the slice on the leaf of Drosera was bathed in much secretion from the inflected tentacles, and was now examined under the microscope.  No perfect grains of chlorophyll could be distinguished; some were shrunken, of a yellowish-green colour, and collected in the middle of the cells; others were disintegrated and formed a yellowish mass, likewise in the middle of the cells.  On the other hand, in the slices surrounded by damp cotton-wool, the grains of chlorophyll were green and as perfect as ever.  My son also placed some slices in artificial gastric juice, and these were acted on in nearly the same manner as by the secretion.  We have seen that bits of fresh cabbage and spinach leaves cause the tentacles to be inflected and the glands to pour forth much acid secretion; and there can be little doubt that it is the protoplasm forming the grains of chlorophyll, as well as that lining the walls of the cells, which excites the leaves.

Fat and Oil.—­Cubes of almost pure uncooked fat, placed on several leaves, did not have their angles in the least rounded.  We have also seen that the oil-globules in milk are not digested.  Nor does olive oil dropped on the discs of leaves cause any inflection; but when they are immersed in olive oil, they become strongly inflected; but to this subject I shall have to recur.  Oily substances are not digested by the gastric juice of animals.

Starch.—­Rather large bits of dry starch caused well-marked inflection, and the leaves did not re-expand until the fourth day; but I have no doubt that this was due to the prolonged irritation of the glands, as the starch continued to absorb the secretion.  The particles were not in the least reduced in size; [page 127] and we know that leaves immersed in an emulsion of starch are not at all affected.  I need hardly say that starch is not digested by the gastric juice of animals.

Action of the Secretion on Living Seeds.

The results of some experiments on living seeds, selected by hazard, may here be given, though they bear only indirectly on our present subject of digestion.

Seven cabbage seeds of the previous year were placed on the same number of leaves.  Some of these leaves were moderately, but the greater number only slightly inflected, and most of them re-expanded on the third day.  One, however, remained clasped till the fourth, and another till the fifth day.  These leaves therefore were excited somewhat more by the seeds than by inorganic objects of the same size.  After they re-expanded, the seeds were placed under