1 8 Chapters in Modern Botany CHAP. 



the excited pitchers than in a test experiment with pepsin 

 from the pig's stomach! This, it must be confessed, seems 

 proving too much, and we shall do well to remember that 

 most samples of prepared pepsin are far from possessing 

 the same digestive potency, still less that of the fresh 

 stomach, not to insist on other sources of fallacy. Still 

 the existence of some appreciable quantity of pepsin seems 

 obvious. Hooker and Tait have shown that fluid removed 

 from a living pitcher into a glass vessel does not digest 

 unless some acid, preferably lactic, be added. During the 

 presence of food, however, they regard the pitcher as con- 

 tinuously stimulated to secrete acid, and to keep up the 

 supply of pepsin. 



Tait also separated a very deliquescent substance from 

 the secretion of this and other insectivorous plants, 

 which he termed azerin. To this he ascribed digestive 

 and antiseptic properties, and also drew attention to its 

 remarkable power of wetting surfaces, just as glycerine or 

 paraffin does. Placing living flies in tubes containing 

 distilled water, Nepenthes fluid, and solution of prepared 

 azerin, he observed that " when those in the tube contain- 

 ing the water touch the surface they remain there as long 

 as -the water is undisturbed without ever getting completely 

 wetted, and that they live for a very long time, as long, 

 perhaps, as in a perfectly dry tube. Those in the other 

 tubes, on the contrary, will become completely wetted in a 

 very few minutes after they touch the surface of the fluid, 

 soon become immersed, and seldom live more than a 

 quarter of an hour or twenty minutes." 



"This must be due to the peculiar wetting property of 

 azerin, enabling the water to enter their tracheae and 

 drowning them. This method of death can be seen in 

 the case of flies placed upon the leaves of Drosera rotundi- 

 folia, for they become wetted in a way which was most 



