Chap. VI.] DIGESTION. 103 



had evidently j-ielded some nutritious matter, for the leaf remained 

 clasped over it for four days; whereas the leaves with bits of the 

 true wing re-expanded on the second day. Any one who will ex- 

 amine the excrement of insect-eating animals will see how powerless 

 their gastric-juice is on chitine. 



Cellulose. I did not obtain this substance in a separate state, 

 but tried angular bits of dry wood, cork, sphagnum moss, linen, 

 and cotton thread. None of these bodies were in the least attacked 

 by tle secretion, and they caused only that moderate amount of 

 inflection which is common to all inorganic objects. Gun-cotton, 

 which consists of cellulose, with the hydrogen replaced by nitrogen, 

 was tried with the same result. We have seen that a decoction of 

 cabbage leaves excites the most powerful inflection. I therefore 

 placed two little square bits of the blade of a cabbage leaf, and four 

 little cubes cut from the midrib, on six leaves of Drosera. These 

 became well inflected in 12 hrs., and remained so for between two 

 and four days; the bits of cabbage being bathed all the time by 

 acid secretion. This shows that some exciting matter, to which I 

 shall presently refer, had been absorbed; but the angles of the 

 squares and cubes remained as sharp as ever, proving that the 

 framework of cellulose had not been attacked. Small square 

 bits of spinach leaves were tried with the same result; the glands 

 pouring forth a moderate supply of acid secretion, and the tenta- 

 cles remaining inflected for three days. We have also seen that 

 the delicate coats of pollen grains are not dissolved by the se- 

 cretion. It is well known that the gastric juice of animals does 

 not attack cellulose. 



Chlorophyll. This substance was tried, as it contains nitrogen. 

 Dr. Moore sent me some preserved in alcohol; it was dried, but 

 soon deliquesced. Particles were placed on four leaves; after 3 hrs. 

 the secretion was acid; after 8 hrs. there was a good deal of in- 

 flection, which in 24 hrs became fairly well marked. After four 

 days two of the leaves began to open, and the other two were then 

 almost fully re-expanded. It is therefore clear that this chloro- 

 phyll contained matter which excited the leaves to a motlerate de- 

 gree; but judging by the eye, little or none was dissolved; so 

 that in a pure state it would not probably have been attacked by 

 the secretion. Dr. Sanderson tried that which I usetl, as well as 

 some freshly prepared, with artificial digestive liquid, and found 

 that it was not digested. Dr. Lauder Bmnton likewise trie<l some 

 prepared by the process given in the British Pharmacopoeia, and 

 exposed it for five days at the temperature of 37 Cent, to digestive 

 liquid, but it was not diminishe<l in bulk, though the fluid accjuiretl 

 a slightly brown colour. It was also tried with the glycerine ex- 

 tract of pancreas with a negative result. Nor docs chloropliyli 

 seem affected by the intestinal secretions of various animals, judg- 

 ing by the colour of their excrement. 



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 col- 

 oured by chlorophyll. My son Francis placed a thin slice of 



