My dear Johnson

I am very much obliged to you for your notes of experiments, for I want to learn all that I can about the castings. The amount of Ammonia surprises me & shows that the castings must serve as a good top-dressing.²

I am doubtful about the percentage of 11^.1 of organic matter, because in speaking lately to David Forbes on the subject, he positively asserted that almost all published analyses of the amount of carbon in vegetable mould were valueless, as the water of composition had not been allowed for. This is not of course expelled by any ordinary drying, but is expelled at the same time that the carbonaceous matters are burnt.—³ Your notes will in all probability come in & be of use some day.— I have not been observing much on subject of late; but I have heard from N. America & Calcutta that the worms threw up castings there as with us; & at Calcutta apparently on a greater scale even than here.—⁴ Some time this autumn I hope to put my notes together & see what results turn up.—

With many thanks | Yours sincerely | Ch. Darwin

I am beginning to suspect that worms perhaps search for animacules or other food, & do not blindly swallow earth for the sake of extracting the commingled organic matter.— I feel certain that a good deal of matter is swallowed, simply for sake of burrowing.—⁵