CHAP. VI. DIGESTION. 125 



were placed on some leaves, and after these had re-expanded, 

 the pieces were carefully examined. Their angles were as 

 sharp as ever, and they did not differ in appearance from the 

 other wing and elytron of the same insect which had been left 

 in water. The elytron, however, had evidently yielded 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 examine 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 the 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 

 Been that a decoction of cabbage-leaves excites the most power- 

 ful 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 secre- 

 tion. 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 tentacles remaining inflected for three days. We have 

 also seen that the delicate coats of pollen grains are not dissolved 

 by the secretion. 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 inflection, 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 chlorophyll contained matter which excited the leaves to a 

 moderate degree ; but judging by the eye, little or none was dis- 

 solved ; so that in a pure state it would not probably have been 

 attacked by the secretion. Dr. Sanderson tried that which I 



