Dear Sir.

Many thanks for your sympathy.¹ If I am ever able to do anything it will be greatly owing to the encouragement you have given me.

Do not trouble yourself about the notes on the sense of smell in cats if they do not come to hand easily.² I remember perfectly the details of the experiment but am not quite certain that I remember the results with absolute fidelity. I will however procure a couple of kittens and bring them up myself, so that I shall be familiar with any peculiarities of disposition or habit which might import an element of doubt or error into the experiments and repeat the trial of the sense of smell in two or three different ways.

I sent you the notes about March 20 1873, as I know from the date of your letter in answer to mine.³

You make no remark upon the case of the rats gnawing through the leaden pipe to get at the water, so I suppose you overlooked it: or it may be familiar to you.⁴

It seems to me to be a very intelligent act: for as in my experience rats never make an experimental hole or waste their energies in any way (I have observed their habits rather carefully during several very long voyages) I think they must have discovered the existence of water in the pipe: but how I cannot conceive. I can easily understand that on board ship they may be led to the knowledge that a cask contains water from the accidental leakage of one and then generalize about others.

I am Dear Sir. | Yours faithfully | Arthur Nicols

Chas Darwin Esq F.R.S etc