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Darwin Correspondence Project

From Joseph Fayrer   30 June 1874

16 Granville Place

30 June 1874

Dear Sir

The following is the result of some experiments made by Dr Brunton and myself with the cobra poison, on ciliary action, and also on muscles.— Some ciliated epithelium from the mouth of a frog was placed under the microscope, divided into two portions, one was moistened with water.— The other with a solution of cobra poison of .03 gramme Poison to 4.6. cubic centimetres of water—1

The motions of ciliae in both were vigorous & those in the poison solution seemed even more vigorous than the other, at first.—

The movements of the ciliae in the poisoned solution soon began to diminish in force— they became languid and ceased altogether in a few minutes—whilst the non-poisoned ciliæ were still acting vigorously. Evidently, the action of the poison was to destroy the power of ciliary motion, having on the first contact perhaps. increased it for a moment. The movements in the poisoned solution lasted, in one experiment, between 15 and 20 minutes. In another experiment they lasted a shorter time—

The following experiment was also made— The Gastrocnemius Muscle of a frog was separated and placed in water   The other gastrocns. muscle of same frog was separated and placed in the solution of Cobra poison—already moistened.— The muscle immediately contracted in marked contradistinction to the muscle placed in the non poisoned fluid.— The experiment was made at 1.25 P.M. at 1.45—the poisoned muscle had lost its irritability not responding to the strongest current, whilst the non poisoned muscle continued to contract vigorously with a weak current (at 11).2 It is obvious therefore, that the action of this poison is to weaken & destroy muscular contractability—3

This experiment must be tried in Amœba.   when it is—you shall know the result.—4

I have written to Dr Weir Mitchell to ask him for some more Crotalus poison5   I will send you some if he complies with my request.— It differs somewhat in its action from the colubrine poison.6

Believe me | Yours very truly | J. Fayrer


The experiments on ciliated epithelium were made on 29 June 1874 and are described in Brunton and Fayrer 1875, p. 273. Fayrer refers to Thomas Lauder Brunton.
The experiments are described in Brunton and Fayrer 1875, pp. 274–5. The gastrocnemius is the muscle between the knee and the foot in the hind leg of a frog.
In Brunton and Fayrer 1875, p. 275, the authors concluded that the poison first stimulated muscle-fibre contraction, but then rapidly destroyed its irritability.
There is no mention of experiments performed on amoebas (single-celled Protozoa of the order Amoebida) in Brunton and Fayrer 1875.
Silas Weir Mitchell, an American doctor, had investigated the effects of snake venom on the nervous system as part of his research on the physiology of the cerebellum (ANB). Crotalus, the genus of rattlesnakes, is native to the Americas.
Venom of rattlesnakes acts on the blood, and in some species on the nervous system, while that of cobras acts mainly on the nervous system. Cobras at this time were classed in the section Colubrinae (see Günther 1858); in modern classificatory systems, they are in the family Elapidae in the infraorder Alethinophidia. Rattlesnakes are in the family Viperidae, also in Alethinophidia.


Reports on results of experiments on effect of cobra poison on animal cilia and muscle.

Letter details

Letter no.
Joseph Fayrer, 1st baronet
Charles Robert Darwin
Sent from
London, Granville Place, 16
Source of text
DAR 58.1: 69–72
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9521,” accessed on 26 June 2019,

Also published in The Correspondence of Charles Darwin, vol. 22