It was well and wisely said, that to know any-thing thoroughly, it must be known in all its details; and, to gain the confidence of the public in the belief of non-contagion in cholera, it is in vain that they are informed that certain alleged facts, brought forward industriously by contagionists, are quite groundless, unless proofs are given showing this to be the case. The public must, in short, have those alleged instances of contagion which have gained currency circumstantially disproved, or they will still listen to a doctrine leading to the disorganization of the community wherever it is acted upon. It is solely upon this ground that these letters have any claim to attention. Dr. James Johnson, of London, has, since my last letter, publicly contradicted, with all the bluntness and energy of honest conviction, the statement by Sir Gilbert Blane, Drs. Macmichael, Hawkins, &c., as to the importation of the cholera into the Mauritius by the Topaze frigate; but _evidence_ is what people want on these occasions, and, relative to the case in question, probably the public will consider what is to be found in my third and fourth letters, quite conclusive. Having again mentioned the Mauritius, I cannot refrain from expressing my great surprise that Mr. Kennedy, who has lately published on cholera, should give, with the view of showing "the dread and confusion existing at the time," a proclamation by General Darling, while he does not furnish a word about the result of the proceedings instituted by that officer, as detailed in my third letter, relative to the non-contagious nature of the disease, a point of all others the most important to the public. As to accounts regarding the confusion caused by the appearance of epidemic cholera, we have had no lack of them in the public papers during many months past, from quarters nearer home.