In a letter called "Compulsory Vaccination," published in 1884, he says: "To obviate it" (small-pox) "by extirpating its causes is good sense; to infuse a new disease without caring to extirpate the causes of the existing disease is a want of common sense." In the letter following, the "Harry" (Dr. Henry) is the boy who boarded with the Newmans, and left snail-shells stuck on a board when he left! He was well known in the world of science as Professor H. Alleyne Nicholson, of Aberdeen. There is no date or address on this letter. "My dear Nicholson, "I have been pressed to make some reply to Dr. Henry's Vaccination pamphlet; but excused myself on the ground that it was not pleasant to me to be in public opposition to him, for he was son of an intimate friend of mine;... I have no special knowledge. I look on it from outside the medical art.... "Now in the contents of the pamphlet I read: 'Small-pox--never produced at present _de novo_.'... "I make sure that it never _could_ have spread, unless the conditions had in all the other places been highly congenial.... Predisposing causes cannot long accumulate and fester, without curdling into vital action. The _provisional assumption_ with me concerning smallpox, is, that wherever its predisposing causes exist, there the disease will not long be absent. In new foci it may meet new influences which modify its aspect, so that medical men do not recognize it; but that signifies not.... "Now, what is Dr. Henry's proof?... "Is there so much as one disease, the origin of which has been recorded scientifically? What he calls 'the primitive origin' of small-pox has not been recorded to us scientifically: yet he does not on that account doubt that it did once arise 'spontaneously.' I judge just in the same way, when it breaks out now in an English country village. What does the 'scientific record' mean? We cannot have a medical man in every room of every house at every moment examining what is under the shirt and shift, with microscope in hand, to see the disease come of _itself_,... Dr. Henry goes on to say, 'and it APPEARS to have spread solely by infection or contagion.' It _appears!_ This is so modest, that the reader fancies he may grant it. But the next words are: 'TWO CONCLUSIONS FOLLOW from this,' etc. etc. In short, he has forgotten that it is only 'it appears,' and fancies that it was c indisputably certain and manifest.' ... After all; if unhealthy conditions are among the prerequisites of small-pox, we have only to remove the unhealthy conditions, and shall not need vaccination (if it were ever so safe): and if you do not remove unhealthy conditions, you are sure of other diseases quite as bad however you may modify the name." _Letters from_ 1872 to 1882 (_to Dr Nicholson_).