This section is from the book "British Dogs: Their Varieties, History, Characteristics, Breeding, Management, And Exhibition", by Hugh Dalziel. Also available from Amazon: British Dogs.
"First, touching Dandies, let us consider with some degree of scientific strictness what a Dandie specially is." The consideration of this question - of what a Dandie Dinmont terrier specially is - has been undertaken by numbers of his ardent admirers, often with a zeal which has overrun knowledge, and with a disregard to that scientific strictness which is guided by facts and forbids the play of imagination, refusing to accept evidence not clearly established, merely because it happens to chime in with interests, prejudices, or preconceived notions.
Had Sir Walter Scott not written "Guy Mannering" there would never have been a breed of dogs known as Dandie Dinmont terriers; had he not created for us that big, burly, honest Liddesdale farmer, with his terriers and his grews, what an unknown quantity of temper would have been directed into other channels, and what fountains of printer's ink would have been saved! There is no class of fanciers so quick to take up a quarrel, or who would fight it out with such tenacity, as those who affect the Dandie; they seem to partake strongly of the pugnacious character of their pets, and, being mostly Scotchmen or Border men, are always ready to "argue the point."
I know a great number of men, that I am very pleased to call my friends, whose enthusiasm on Dandie Dinmont subjects is so intense that were it not that they are so cool headed, reasonable, and shrewd in dealing with all other topics, lunatico inquirendo would naturally occur to the mind; with many it is only necessary to whisper Harry or Sir Douglas in their ear to produce a similar effect to shaking a red rag before a mad bull; not being quite free from the taint myself, I can speak the more freely of a weakness that has characterised in a special manner a large proportion of Dandie Dinmont fanciers. Time and mutual gatherings at shows and elsewhere has, however, brought the opinions of all nearer together.

REV. T. MOSSE'S DANDIE DINMONT "SHAMROCK" (K.C.S.B. 3089). Sire Mr. Hodges' Mustard - Dam Mr. Broadwith's Vic.
The fact is, in my opinion, we have claimed too much for the dog; enthusiasm has idealised him, and strong desire has created good qualities as inherent and never wanting in the breed, but which are not always found. It is a mistake to claim for every Dandie all the best attributes of a terrier; as a class there is no dog more game, and with gameness they generally possess considerable intelligence and tractability; but I have known Dandies of the bluest blood that were worth very little. Although, speaking broadly, as a terrier he is unexcelled; a good specimen has all the courage and perseverance of the bull terrier, and is under far better control, and in comparison with his cousin, the Bedlington, his temper alone gives him the palm. I think no one can reasonably object to my speaking of the Bedlington as a relation of the Dandie - the two breeds have so many points in common that it appears to me impossible to ignore their relationship.
Another point much insisted on is absolute purity of descent from Dandie Dinmont's dogs - well, I confess myself a sceptic, and I think this has been made too much of. I have little faith in the absolute purity of any specimen living, and I must add I think it a matter of very little consequence; there is abundance of proof that the very great bulk of our Dandies have at least a large proportion of the blood of Mr. Davidson's terriers in them, but to suppose that they have been kept absolutely free from crosses, whether occurring by accident or design, is to take up with the improbable. When the Dandie Dinmont terrier stud book is compiled we may have more light thrown on this subject, but I confess I have little faith in many of the oral traditions on which we are asked to place implicit confidence.
I have a letter before me in which the writer says he was, when a boy, on the most intimate terms with Hugh Purves, one of the few who had dogs direct from Charlieshope, and assisted in keeping up the old breed; and my correspondent says that Purves more than once used a brindled bull terrier to his Dandie bitches, and I think it is rather unreasonable to ask us to believe that the Dandie of the day is absolutely, and without the slightest admixture, descended from Pepper and Tar.
The Dandie Dinmont Terrier Club have drawn up a standard of points, and if a dog agrees with that standard, possessing all the points required, it is of little consequence whether his ancestors were whelped at Ellwan foot or in Coaly Newcastle. Purity must, in speaking of dogs, always be used comparatively; there is not a single breed in existence worth a Spratt'sbiscnit that can claim absolute purity. We have got them to their present state of high development by careful selection and judicious crossings, and it should be quite sufficient for us to know that there are hundreds of Dandies now living that are to all intents and purposes pure bred, in so far as they have at least more or less of the blood of Dandie Dinmont's Mustards and Peppers, and have the recognised characteristics of the breed so fixed in themselves as to be depended on to reproduce the-same with almost absolute faithfulness. Much as has been written anent Dandie Dinmont terriers, that much has for the most part been in ephemeral form, chiefly in the various contributions to the controversies on the subject that have been raised from time to time in the newspapers (notably in the "Field" and the "Country"), and a good deal of information and many valuable opinions are therein met with.
The Rev. J. C. Macdona was, I believe, the first to give publicity to the following unquestionably important document, which he met with in researches he made some ten or twelve years ago into the early history of the breed; it is described as being in the handwriting of James Davidson, with his initials attached, written on old hand-made letter paper, yellow with years and bearing all the evidences of being genuine. The memorandum was originally sent by Mr. Davidson to the Hon. George H. Bailie, of Mellerstain, and is as follows:-
 
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