54 



PHYSIOLOGY 



CHAP. 



animal substances to a real digestion. Papain, an enzyme which 

 has the same properties as pepsin, has been extracted from Carica 



FIG. 0. M inland pudico. During the day the leaves are extended, as in A ; when stimulated 

 by shaking or touching, they close up, drooping backwards, as in Ji. After chloroform 

 narcosis this reaction does not take place. 



papaja. The juices of the leaves of Nepenthes, Drosera, and Dionea 

 (Figs. 11 and 12) digest meat to the great advantage of the plant. 

 We know further that plants, like animals, accumulate sugar, 



starch, oil, and proteins 

 as reserve nutritive ma- 

 terials, and, for nutritive 

 purposes and to bring 

 them into circulation, 

 submit them to a regular 

 digestion by the action 

 of certain enzymes, such 

 as diastase, invertin, 

 emulsin, and the peptic 

 or hydrolytic ferments. 



After Lavoisier (17 77) 

 had demonstrated that 

 animals absorb oxygen 

 and exhale carbonic acid r 

 and the Dutch Ingen- 

 housz, and almost contemporaneously the Genevans Senebier and 

 Th. de Saussure (1800), had discovered that green plants reduce 

 the carbonic acid of the air by assimilating carbon and emitting 

 oxygen, a theory was involved which predicated a functional 

 antagonism between plants and animals. By storing up the 



FIG. 10. --T.eaf of Dioitca mn^ipnh'. (Darwin.) Tlie 

 upper surface of the leaf shows the bristles that react 

 on the slightest contact with an insect, provoking im- 

 mediate closure of the two halves of the leaf, and 

 capture of the insect, which is then digested by the 

 secretion from the glands upon the surface of the leaf. 



