To J. S. Burdon Sanderson   13 October 1874

My dear D^r. Sanderson

Many thanks for your suggestion, but I doubt whether it is sufficient.¹ The tentacles close very slowly over the 5 specified substances, & this might be accounted for by their pure state.² But the important fact is that they subsequently re-expand so much more quickly than over minute insects, meat albumen etc. It is chiefly this latter fact which makes me conclude that the 5 substances are but little exciting & probably not very nutritious. I made so many experiments with Gelatine that I can hardly doubt that this conclusion is true with this substance.³ Klein speaks (Handbook Phys. p. 445) as if areolar (or connective) tissue & the fibrous basis of bone, were of a gelatinous nature, & this made me suppose that perhaps fibrin & fibro-cartilage were likewise allied to gelatine; & as gelatine is so little nutritious to animals, I imagined that the little action of these 5 substances on drosera might be thus explained.⁴ My best plan would be, I think, merely to call attention to the small power of the 5 substances on drosera, & to say (if you admit the truth of my inference from Klein) that at least areolar tissue & the fibrous basis of bone were allied to gelatine, & that gelatine was very little nutritious to animals—

I fear from what you say that I may not add that fibrin are likewise allied to gelatine: do you know what is the nature of fibro-cartilage?⁵ If you have anything further to remark I sh^d be grateful for a note—

With many thanks, | yours very sincerely | Ch. Darwin