Those who have watched the course of matters connected with cholera in this country, have not failed to perceive, for some time past, the intent and purport of the assertion so industriously put forth--that the disease might be introduced by people in perfect health; and we have just seen how this _ruse_ has been attempted to be played off at Sunderland, as the history of such matters informs us has been done before in other instances, and public vengeance invoked most _foully and unjustly_ upon the heads of guiltless persons in the Custom House or Quarantine Department, for "permitting a breach of regulations;" but the several pure cases of spasmodic cholera, in many parts of England besides Sunderland, long before--months before--the arrival of _the_ ship (as shewn in a former letter) leave no pretence for any supposition of this kind. I request that the public may particularly remark, that, frequently as those cases have been cited as proofs of the absurdity of _expecting the arrival_ of the disease by a ship, THEIR IDENTITY HAS NEVER ONCE BEEN DISPUTED BY THOSE MOST ANXIOUS TO PROVE THEIR CASE. No; the point has, in common parlance, been always _shirked_; for whoever should doubt it, would only hold himself up to the ridicule of the profession, and to admit it would be to give up the importation farce. Others have remarked before me that, though a very common, it is a very erroneous mode of expression, to say of cholera, that _it has travelled_ to such or such a place, _or has arrived_ at such or such places, for it is _the cause_ of the malady which is found to prevail, for a longer or shorter time, at those different points. It cannot be expected that people should explain such matters, for, with regard to them, our knowledge seems to be in its infancy, and "we want a sense for atoms." However, as people's minds are a good deal occupied upon the point, and as many are driven to the idea of contagion in the face even of evidence, from not being able to make any thing of this _casse-tete_, the _best guess_ will probably be found in the quotation from Dr. Davy, at page 19.