315 DARWINIAXA. 



stance far beyond the resources of the most skillful 

 chemist ; but in a foot-note he admits that " now the 

 spectroscope has altogether beaten Drosera / for, ac- 

 cording to Bunsen and Kirchhoff, probably less than 

 the goooftoooo * a g ram of sodium can be thus 

 detected." 



Finally, that this highly-sensitive and active living 

 organism absorbs, will not be doubted when it is 

 proved to digest, that is, to dissolve otherwise insol- 

 uble animal matter by the aid of special secretions. 

 That it does this is now past doubting. In the first 

 place, when the glands are excited they pour forth an 

 increased amount of the ropy secretion. This occurs 

 directly when a bit of meat is laid upon the central 

 glands ; and the influence which they transmit to the 

 long-stalked marginal glands causes them, while incurv- 

 ing their tentacles, to secrete more copiously long be- 

 fore they have themselves touched anything. The 

 primary fluid, secreted without excitation, does not of 

 itself digest. But the secretion under excitement 

 changes in Nature and becomes acid. So, according 

 to Schiff, mechanical irritation excites the glands of 

 the stomach to secrete an acid. In both this acid ap- 

 pears to be necessary to, but of itself insufficient for, 

 digestion. The requisite solvent, a kind of ferment 

 called pepsin, which acts only in the presence of the 

 acid, is poured forth by the glands of the stomach only 

 after they have absorbed certain soluble nutritive sub- 

 stances of the food; then this pepsin promptly dis- 

 solves muscle, fibrine, coagulated albumen, cartilage, 

 and the like. Similarly it appears that Z>>'0s<?ra-glands, 

 after irritation by particles of glass, did not act upon 



