INFLUENCE OF EARTHWORMS ON SOIL REACTION. 421 
In the course of these estimations no attempt was made to distinguish 
between the various British species of Earthworm, and it is not improbable 
that these are capable of modifying the reaction in different degrees. Even, 
however, were the same species involved, the effect on different soils of the 
same original acidity might be expected to vary. For, though many soils 
are strongly buffered, the degree of the buffering is often very different in 
soils of the same original reaction. 
As to the manner in which earth worms effect the change, Ray Lankester 
showed in 1864 (Q J. M. S. vol. iv. p. 258) that the @sophagus of the earth- 
worm bears three paired diverticula whose epithelium secretes calcareous 
particles (ef. also Beddard, Camb, Nat. Hist. p. 359), and Darwin long ago 
suggested that these might serve to neutralize the so-called Humic acids. 
That this suggestion was justified, the above results would appear to show 
fully. However, the final proof was obtained by placing worms in a soil of 
known reaction and determining that of the wormeasts formed. The soil was 
carefully mixed, but at the time the wormeasts were collected the soil reaction 
showed a small range, namely from pH 6°6 to pH 6°8 with 6°66 as the mean 
value (specific acidity=2'25). The wormcasts exhibited a range from 
pH 6:9 to pH 7:1 with a mean value of pH 7 (specific acidity =1). The 
experimental conditions here precluded the possibility of the surface soil 
being mixed in the digestive tract of the worm with subsoil substance. The 
writer has elsewhere shown (loc. cit, Annals of Botany, vol. xxxvi.) that 
the later stages of decay are less acid than the earlier ones, and it is quite 
possible that during the process of digestion the chemical changes which the 
soil undergoes may lead to a decrease in acidity, but analyses of soil and 
wormcasts with respect to the carbonate content have shown that the latter 
normally contain an appreciably higher percentage than the soils from which 
they are respectively derived (cf. Table VL.). This is shown graphically in 
fie. 3. 
TABLE VI. 
Carbonate Content of Soils and Wormcasts. 
Per cent. Per cent. | 
Carbonates Carbonates of | 
of Soil. Wormcasts. 
Festuca-Agrostis cese 0:022-0:05 0047-0707 | 
Polytrichum-Agrostis .......,...... 0:02 av. | 0:08 av. | 
Markyate Scrub .................. 0:20 av. | 026 av. | 
Colney Heath. Loe. A ............ 005-008 | 0120% | 
” » Loc. B ............ (00704 av. | 0-09 av. 
Quercus Robur-Corylus. Wood ... -| 0:02-0:10 0:06-0:17 
Hertford Heath ..........,.,....... | 0:02 av. 0:07 av. 
Mean values ,,...,.... | 0:050 °/, 0:124 °/, 
