Dear M^r Darwin,

On carefully considering the fact stated in your letter of the 9^th.¹ namely that fibrin, areolar tissue, and gelatine and the fibrous basis of bone, differ from meat and albumen in not exciting the leaves of Drosera, it appears to me that the differences may be dependent on the circumstance that the former are used in a prepared (i.e washed) condition, the others in a crude (i.e. unwashed) state—and consequently that in the latter nitrogenous stuff soluble in water, (socalled water-extractive) is present, in the former absent. Inasmuch as it is a necessary condition for chemical excitation that the exciting material should be soluble, this may explain the difference. If this surmise is right, thoroughly washed meat would act on the leaf less excitingly than unwashed.²

With reference to the question whether a dog would perish sooner when fed on gelatin than when fed on fibrin, there is no doubt that it would, for although fibrin has not been compared with gelatin experimentally, albuminous foods have been so compared, & it has been found that feeding on gelatin results in inanition much more quickly than feeding exclusively on albuminous stuff.³

Please let me know whether you think that my suggestion appears to you satisfactory & whether you w^d. like me to make any experiment with reference to it.

I think the expression “fibrous basis of bone” is a perfectly correct & usual expression⁴

I am, my dear M^r Darwin | very faithfully yours | J S B Sanderson