CHAP. XVI. SECRETION, ABSORPTION, DIGESTION. 389 



see that objects not containing soluble matter have 

 little or no power of exciting the glands to secrete. 

 Non-nitrogenous fluids, if dense, cause the glands to 

 pour forth a large supply of viscid fluid, but this is 

 not in the least acid. On the other hand, the secre- 

 tion from glands excited by contact with nitrogenous 

 solids or liquids is invariably acid, and is so copious 

 that it often runs down the leaves and collects 

 within the naturally incurved margins. The secre- 

 tion in this state has the power of quickly dissolving, 

 that is of digesting, the muscles of insects, meat, 

 cartilage, albumen, fibrin, gelatine, and casein as 

 it exists in the curds of milk. The glands are 

 strongly excited by chemically prepared casein and 

 gluten; but these substances (the latter not having 

 been soaked in weak hydrochloric acid) are only 

 partially dissolved, as was likewise the case with 

 Prosera. The secretion, when containing animal 

 matter in solution, whether derived from solids 

 or from liquids, such as an infusion of raw meat, 

 milk, or a weak solution of carbonate of ammonia, 

 is quickly absorbed ; and the glands, which were 

 before limpid and of a greenish colour, become brownish 

 and contain masses of aggregated granular matter. 

 This matter, from its spontaneous movemen ts, no doubt 

 consists of protoplasm. No such effect is produced 

 by the action of non-nitrogenous fluids. After the 

 glands have been excited to secrete freely, they cease 

 for a time to secrete, but begin again in the course of 

 a few days. 



Glands in contact with pollen, the leaves of other 

 plants, and various kinds of seeds, pour forth much 

 ucid secretion, and afterwards absorb matter probably 

 of an albuminous nature from them. Nor can the 

 benefit thus derived be insignificant, for a considerable 



