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 secretion 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 unexcited 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 [page 88] appears to be to a certain extent antiseptic, as it checks the appearance of mould and infusoria, thus preventing for a time the discoloration and decay of such substances as the white of an egg, cheese, &c.  It therefore acts like the gastric juice of the higher animals, which is known to arrest putrefaction by destroying the microzymes.

[As I was anxious to learn what acid the secretion contained, 445 leaves were washed in distilled water, given me by Prof.  Frankland; but the secretion is so viscid that it is scarcely possible to scrape or wash off the whole.  The conditions were also unfavourable, as it was late in the year and the leaves were small.  Prof.  Frankland with great kindness undertook to test the fluid thus collected.  The leaves were excited by clean particles of glass placed on them 24 hrs. previously.  No doubt much more acid would have been secreted had the leaves been excited by animal matter, but this would have rendered the analysis more difficult.  Prof.  Frankland informs me that the fluid contained no trace of hydrochloric, sulphuric, tartaric, oxalic, or formic acids.  This having been ascertained, the remainder of the fluid was evaporated nearly to dryness, and acidified with sulphuric acid; it then evolved volatile acid vapour, which was condensed and digested with carbonate of silver.  “The weight of the silver salt thus produced was only .37 gr., much too small a quantity for the accurate determination of the molecular weight of the acid.  The number obtained, however, corresponded nearly with that of propionic acid; and I believe that this, or a mixture of acetic and butyric acids, were present in the liquid.  The acid doubtless belongs to the acetic or fatty series.”

Prof.  Frankland, as well as his assistant, observed (and this is an important fact) that the fluid, “when acidified with sulphuric acid, emitted a powerful odour like that of pepsin.”  The leaves from which the secretion had been washed were also sent to Prof.  Frankland; they were macerated for some hours, then acidified with sulphuric acid and distilled, but no acid passed over.  Therefore the acid which fresh leaves contain, as shown by their discolouring litmus paper when crushed, must be of a different nature from that present in the secretion.  Nor was any odour of pepsin emitted by them. [page 89]