My dear Sir,

I enclose a slip of Litmus paper, from which you will observe that the fluid contained in the phial you have sent to me, is acid—²

A great part of the tenacious mass contained in the phial consists of bundles of that filamentous structure, to which I alluded in my account of your slide; but which I could ⁠⟨⁠not⁠⟩⁠ define or account ⁠⟨⁠for the⁠⟩⁠ putrifactive chang⁠⟨⁠es that⁠⟩⁠ had taken place. These bundles of minute filaments, appear to me to be referable to some form of Leptothrix; probably L buccalis, which is an Alga found on the mucous membrane of the Tongue and mouth, but accumulating occasionally in the stomach and bowels.³

I see these bundles of filaments on my slides ⁠⟨⁠along⁠⟩⁠ with numerous epi⁠⟨⁠theliu⁠⟩⁠m scales from the ⁠⟨⁠mouth⁠⟩⁠— These scales are seen enve⁠⟨⁠loped by⁠⟩⁠ molecular ma⁠⟨⁠tter and⁠⟩⁠ debris from w⁠⟨⁠hich⁠⟩⁠ bundles of filaments ⁠⟨⁠    ⁠⟩⁠cied

I enclose a rough sketch of a bundle attached to molecular matter investing an epithelium scale; a⁠⟨⁠nd⁠⟩⁠ of a group of Torula cell⁠⟨⁠s,⁠⟩⁠ two buccal or saliva cells, and the minute cells, probably the spores of Leptothrix.⁴

As I have already stated—medical opinion ⁠⟨⁠2 words⁠⟩⁠ to any ⁠⟨⁠2 words⁠⟩⁠ as to the ⁠⟨⁠    ⁠⟩⁠ of decreasing those parasites—⁵

Believe me— | my dear Sir— | sincerely yours | John Goodsir.

Charles Darwin Esq.