My dear Sir,

I regret extremely that I have allowed myself to leave your letter of the 26^th of last month so long unanswered.² It is not so much that I have not had time as that by circumstances my thoughts have been forced to take directions quite away from the subjects which most interest me. Now I am again free.

I am much pleased to learn 1 that drosera digests properly and 2 that it is unable to distinguish between infusions containing albumin of vegetable or animal origin.³

As regards the frog I can reply very definitely to the question “at what temperature are cold blooded animals killed”.

A frog under ordinary circumstances begins to be very much distressed at 85^o4 (if immersed in water the temp. of which is gradually raised).

Above 85^o up to 95^o the distress increases i.e. it makes more & more violent efforts to escape, which efforts eventually assume the convulsive character   Above 95^o. the muscles become rigid & the animal dies stiff.

I do not think that the phenomena observed in Drosera when the leaves are heated to 145^o. to 150^o.⁵ can be regarded as those of heat rigor. At so high a temperature you come within the range of another kind of change viz that of coagulation of albumin by heat. Albumin coagulates at about 155^o, but in presence of acids the temp. of coagulation is always lower, so that I should be inclined to regard the fact that the glands become white and opaque at 145^o. as a result of this change.⁶

The most important facts as regards the physiological action of high temp^re. on Drosera, seem to me to be those which prove that within the range of ordinary temp. (i.e. of the temperatures to which the plant is accustomed) the excitability of the glands increases with the temperature   The establishment of these facts seems to be quite sufficient to prove that the relation between the contractile function in Drosera and temperature is the same as in the animal kingdom.

It has occurred to me that it would be very interesting to show that when the Drosera leaf is excited the same electrical changes occur as in muscle & nerve. If you think so, it would not be difficult to plan an experiment.⁷ The fact if it can be demonstrated, would afford additional evidence of of the identity of the processes.

I am, My dear M^r Darwin | very truly yours | J B Sanderson