CHAP. VI. DIGESTION. 131 



prepared casein, which is said to consist of two sub- 

 stances ; and although SchifT asserts that casein in 

 this state is not attacked by gastric juice, he might 

 easily have overlooked a minute quantity of some 

 albuminous matter, which Drosera would detect and 

 absorb. Again, fibre-cartilage, though not properly 

 dissolved, is acted on in the same manner, both by 

 the secretion of Drosera and gastric juice. But this 

 substance, as well as the so-called hcernatin used by 

 me, ought perhaps to have been classed with indi- 

 gestible 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 

 likewise acts only in the presence of an acid ; for we 

 have seen that when the secretion is neutralised by 

 minute drops of the solution of an alkali, the diges- 

 tion of albumen is completely stopped, and that on 

 the addition of a minute dose of hydrochloric acid it 

 immediately recommences. 



The nine following substances, or classes of sub- 

 stances, namely, epidermic productions, fibre-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 extracted from the mucin, 

 pepsin, and chlorophyll, used by me, both by the 

 secretion and by artificial gastric juice. 



The several substances, which are completely dis- 

 solved by the secretion, and which are afterwards 

 absorbed by the glands, affect the leaves rather dif- 

 ferently, They induce inflection at very different 



