THE MAD-STONE.--The reference of _The Washington Union_ to the mad-stone (one of which is now in the possession of the family of the late Mr. John King Churchill, in Richmond, Va.) has drawn articles upon the subject from several of our cotemporaries. _The Petersburg Intelligencer_ has been shown one, in the possession of Mr. Oliver, who resides in Petersburg, and, it is said, has several certificates of cases in which it has been successfully used for the bite of a mad dog. It is rectangular in shape, with parallel sides and polished surfaces, traversed by dark-gray and brown streaks, and about a size larger than half a Tonquay bean, except that it is not near so thick. Upon being applied to the wound of the patient, says _The Intelligencer_, it soon extracts the virus, which, it is said, may be distinctly seen in the water, into which it is repeatedly dipped during the operation. _The Portsmouth Globe_ says: “We were raised--‘brought up’ is, perhaps, the word--in Petersburg, Va., and among our very earliest recollections is one concerning a cure from hydrophobia, made through the agency of a mad-stone. The person, whoever it was that was bit by a rabid dog, went to Williamsburg, in this State, where it was said that a mad-stone was located, and came back well, and was never troubled either with madness or its symptoms. Our next notice of the subject was when two individuals in Petersburg were bitten by mad dogs. One, we think, lived in Halifax street, and his father believing the mad-stone a humbug, refused to let his son go and try it. He was seized with the fits, after the usual medicinal agents had failed, and died in great agony. The other visited the mad-stone--still then at Williamsburg--and entirely recovered. The next case was this: We were travelling from Paineville, Amelia County, to Farmville, Prince Edward County, Va., and stopped at a blacksmith’s house to get dinner. In the course of conversation, he said he had been bit by a mad dog, that had destroyed by its bite a number of cattle, sheep and hogs, and that he hastened at once to Williamsburg; that, on the way, he had suffered much from the bite, but after the application of the stone, he had got relief and suffered none since. ‘That bite,’ said he, laying much emphasis on the cost, ‘_cost_ me nearly a _hundred_ dollars.’ “Such is all that we remember concerning the mad-stone.” As a pendant, we give a “slip” from the Richmond (Virginia) _Penny Post_ for August 12, 1854. The description, if it may be so called, of the stone referred to is remarkable: “as large as a piece of chalk,” and “almost indescribable:”