Chap. VI. DIGESTION. 87 



these fourteen leaves had become more or less in- 

 flected, I again tested the secretion, selecting glands 

 which had not as yet reached the centre or touched 

 any object, and it was now plainly acid. The degree 

 of acidity of the secretion varied somewhat on the 

 glands of the same leaf. On some leaves, a few ten- 

 tacles did not, from some unknown cause, become in- 

 flected, as often happens ; and in five instances their 

 secretion was found not to be in the least acid; 

 whilst the secretion of the adjoining and inflected 

 tentacles on the same leaf was decidedly acid. With 

 leaves excited by particles of glass placed on the 

 central glands, the secretion which collects on the 

 disc beneath them was much more strongly acid 

 than that poured forth from the exterior tentacles, 

 which were as yet only moderately inflected. When 

 bits of albumen (and this is naturally alkaline), or 

 bits of meat were placed on the disc, the secretion 

 collected beneath them was likewise strongly acid. 

 As raw meat moistened with water is slightly acid, I 

 compared its action on litmus paper before it was 

 placed on the leaves, and afterwards when bathed in 

 the secretion ; and there could not be the least doubt 

 that the latter was very much more acid. I have 

 indeed tried hundreds of times the state of the secre- 

 tion on the discs of leaves which were inflected over 

 various objects, and never failed to find it acid. We 

 may, therefore, conclude that the secretion from un- 

 excited leaves, though extremely viscid, is not acid or 

 only slightly so, but that it becomes acid, or much 

 more strongly so, after the tentacles have begun to 

 bend over any inorganic or organic object ; and still 

 more strongly acid after the tentacles have remained 

 for some time closely clasped over any object. 



I may here remind the reader that the secretion 

 5 



