108 DROSEBA EOTUNDIPOLIA. [Chap. VL 



consist of two substances; and although Schiff asserts that 

 casein in this state is not attacked by gastric juice, he might 

 easily have overlooked a minute quantity of some albumi- 

 nous matter, which Drosera would detect and absorb. Again, 

 fibro-cartilage, though not properly dissolved, is acted on in 

 the same manner, both by the secretion of Drosera and gas- 

 tric juice. But this substance, as well as the so-called 

 hsematin used by me, ought perhaps to have been classed with 

 indigestible substances. 



That gastric juice acts by means of its ferment, pepsin, 

 solely in the presence of an acid, is well established; and 

 we have excellent evidence that a ferment is present in the 

 secretion of Drosera, which likwise acts only in the pres- 

 ence of an acid ; for we have seen that when the secretion is 

 neutralised by minute drops of the solution of an alkali, the 

 digestion of albumen is completely stopped, and that on 

 the addition of a minute dose of hydrochloric acid it imme- 

 diately recommences. 



The nine following substances, or classes of substances, 

 namely epidermic productions, fibro-elastic tissue, mucin, 

 pepsin, urea, chitine, cellulose, gun-cotton, chlorophyll, 

 starch, fat, and oil, are not acted on by the secretion of 

 Drosera; nor are they, as far as is known, by the gastric 

 juice of animals. Some soluble matter, however, was ex- 

 tracted from the mucin, pepsin, and chlorophyll, used by me, 

 both by the secretion and by artificial gastric juice. 



The several substances, which are completely dissolved by 

 the secretion, and which are afterwards absorbed by the 

 glands, affect the leaves rather differently. They induce in- 

 flection at very different rates, and in very different de- 

 grees; and the tentacles remain inflected for very different 

 periods of time. Quick inflection depends partly on the 

 quantity of the substance given, so that many glands are 

 simultaneously affected, partly on the facility with which it 

 is penetrated, and liquefied by the secretion, and partly on 

 its nature, but chiefly on the presence of exciting matter 

 already in solution. Thus saliva, or a weak solution of 

 raw meat, acts much more quickly than even a strong solu- 

 tion of gelatine. So again leaves which have re-expanded, 

 after absorbing drops of a solution of pure gelatine or isin- 

 glass (the latter being the more powerful of the two), if 



