To George Gulliver 18 December 
Down Bromley Kent
I thank you sincerely for your extremely kind letter, & for all the great trouble you have taken in explaining to me (& it was very necessary) how to send the blood.—1 I send by this Post, blood of the Barb, short-faced Tumbler & Dragon, which latter is nearly as good as that of Carrier.— These are 3 very distinct breeds: unfortunately I have not one common blue chequered rock or dovecot pigeon; nor is one kept, within half a dozen miles of this place: if you could possibly get blood of this, I shd. think it would be very desirable, as a standard.
I shall soon have Spanish Runts & Turbits,2 & if your examination gives any hope of anything curious I would send examples of them, & of Fantails & Pouters, & then you would have blood of every main breed.— I shall be very curious to hear the result.— With respect to your very kind offer of sending me the Book edited by you;3 if you are quite sure you can spare a copy, I shd. be very glad of it, for the fact stated by you of the difference in the blood of congenerous animals seems to me very curious.
I am nearly sure that the Passenger Pigeon & Turtle dove have interbred, so that if blood of the former differs from the latter, it is eminently curious.—4 I have often observed that when one single character in a species differs in a marked & extraordinary degree from that of its congeners, this character is apt to be variable, especially if several individuals from different habitats are observed: I presume that you examined the blood of only single individuals in the cases enumerated by you, in which the blood presented very marked characters; but I shd. be glad to hear whether you noticed any unusual variability in the corpuscles in these particular species.—
I am almost sure I have read in Zoolog. Proceeding an account by you of the Blood of the different races of Dogs;5 & if I am right, I have certainly marked the passage, & shall meet with it again, when going over the Books read of late years.— Nevertheless I shd. be very much obliged if you would inform me, whether it has so happened that you have, since such publication, examined the blood of any other varieties or Breeds of Dogs or of any other domesticated animals.
I fear you will think me quite unreasonable, but I would ask whether it would not be worth while to look at the Blood of Bantams, Cochin-Chinas, Dorking or Game; ie, of 2 or 3 of the most strongly marked races or species. You will see that the kindness of your note has made me greedy in my enquiries.—6
Pray believe me, my dear Sir, with very sincere thanks, | Your’s truly obliged | Charles Darwin
Sends blood of pigeons for examination. Discusses variation of blood in related animals.
Would like copy of book edited by GG [The works of W. Hewson (1846)].
Suggests investigation of blood in varieties of domesticated animals.
Please cite as
Darwin Correspondence Project, “Letter no. 1796,” accessed on 27 September 2016, http://www.darwinproject.ac.uk/DCP-LETT-1796