Cuar. VL] DIGESTION. 103 
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 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 
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 dissolved; so that in a pure state it would not 
probably have been attacked by the seeretion. Dr. Sanderson tried that 
which I used, as well as some freshly prepared, with artificial digestive 
liquid, and found that it was not digested. Dr. Lauder Brunton 
likewise tried some prepared by the process given in the British Phar- 
macopeia, and exposed it for five days at the temperature of 37° 
Cent. to digestive liquid, but it was not diminished in bulk, though 
the fluid acquired a slightly brown colour. It was also tried with 
the glycerine extract of pancreas with a negative result. Nor does 
chlorophyll seem affected by the intestinal secretions of various animals, 
judging by the colour of their excrement. . 
It must not be supposed from these facts that the grains of 
chllorophyll, 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 
