My dear Carpenter

I read two days ago your article in the last Contemporary, & I must have the pleasure of expressing my extreme interest & admiration at it. This will cause you no trouble, as this note obviously requires no answer. The case of the 3 species of Protozoon (I forget the name) which apparently select differently sized grains of sand &c is almost the wonderful fact I ever heard of.² One cannot believe that they have mental power enough to do so, & how any structure or kind of viscidity can lead to this result passes all understanding.—

Your views on the function of the brain are also profoundly interesting, but I know not enough for my opinion to be worth a fraction of a farthing. I was, however, speculating on this subject, when writing on Expression; & came to the conclusion that when we actually tasted & thought of a sour taste, the same or some closely related part of the brain must be affected. Had I then known of your views I sh^d have omitted the first alternative.³

I thank you heartily for the pleasure derived from your article & remain, yours very sincerely | Ch. Darwin