OCR Text |
Show 240 DISINTEGRATION CrrAP. V. eartL,1_ ; an d I't I·s this process which . gives t.o vegetab l e mou ld its un. iform dar.k tint. It IS known that various lnnds of aCids are gene-rated b y the decay of vegeta. ble matter ; and f rom the contents of the intestines .o f worms and from their castings being acid,. It ~eoms pro-bable that the process of digestiOn Jnduces an anaI ogous ch eml.cal chanoo- e in the swallowed, triturated, and half-decayed leaves. The large quantity of carbonate of lime secreted by the calciferous glands apparently serves to neut:'alise the acids thus generated; for_ the digcs:Ive fluid of worms will not act unless It be alk~h~ e. As the contents of the upper part of thmr Intestines are acid, the acidity can hardly be due to the presence of uric acid. vVe m~y therefore conclude that the acids in the ahmen_tary canal of worms are formed during the digestive process; and that probabl~ the~ arc nearly of the same nature as those In ordmary mould or humus. The latter are well known to have the power of de-oxidising or di ssolving per-oxide of iron, as may bo seen wherever peat overlies red sand, or where a rotten root penetrates such sand. Now I kept so~ne worms in a pot filled with very fine reddJt)h CHAP. v. AND DENUDATION. 241 sand, consisting of minute particles of silex coated with the red oxide of iron ; and the burrows, which the worms made through this sand, were lined or coated in the usual manner with their castings, formed of the sand mingled with their intestinal secretions and the refuse of the digested leaves; and this sand had almost wholly lost its red colour. When small portions of it were placed under the microscope, mo~;t of the grains were seen to be transparent and colourless, owing to the dissolution of the oxide; whilst almost all the grains taken from other parts of the pot were coated with the oxide. Acetic acid produced hardly any effect on this sand ; and even hydrochlorjc, nitric and sulphuric acid , diluted as in the Pharn1acopceia, produced less effect than did the acids in the intestines of the worms. Mr. A. A. Julien has lately collected all the extant information about the acids generated in humus, which, according to some chemists, amount to more than a dozen different kinds. 'rhese acids, as well as their acid salts (i.e., in combination with potash, soda, and ammonia), act energetically on R |