So much for the skiagraphic findings in chronic gout, and now to discuss their valency as aids to diagnosis of this arthritic disorder. The chief controversy centres around the significance of the _focal areas of rarefaction_ which have been found in the bones of the wrists, hands, ankles, and feet of gouty subjects. Here we may comment on one grave handicap, viz., the lack of certainty as to whether the cases radiographed by different observers were true instances of _gouty_ arthritis. To justify our expression of doubt we may take, for example, the series reported by Drinberg and Jacobsohn. The said “transparent areas” were present in all the eighteen cases, but the presence of _tophi_ was only established in three. Now, as McClure and McCarty rightly contend, “since the tophus is the only universally accepted pathognomonic sign of gout, for studies of that disease only those patients should be chosen in whom tophi are found, and sodium urate crystals from them microscopically demonstrated.” No one can, I think, gainsay the legitimacy of this stipulation. In accordance with their contention, McClure and McCarty record their radiographic findings in a series of cases all of which exhibited _tophi_, and from which sodium urate crystals were isolated. Now, in all these cases the _focal areas of diminished density_, generally held to be peculiar to gout, were present; but they add that “similar changes were present in two other cases which were clinically gout, but in which no tophi were demonstrated.” Also “in another case without tophi, but which was clinically gout, the focal areas of decreased bony density were not found.” In addition, they examined the skiagrams of 100 cases of _chronic arthritis_ which “had not been diagnosed clinically as _gout_.” In thirteen of the examples “the focal areas of decreased density, the so-called gouty bony changes, were found, and were fully as well defined as in the cases of true gout.” Judging from the skiagraphic appearances, there seemed no reason to suppose that the factors responsible for the production of these rarefied areas were in any way different from those at work in true gout. Now, most authorities have claimed that the bony changes were due to _uratic deposits_ in the bones; but it is at least possible that their origin may be otherwise explained. Thus Nichols and Richardson have shown that, given _focal absorption of lime salts_, changes apparently identical with those currently attributed to the presence of _tophi_ may result. These same, though they may not be demonstrable either macroscopically or microscopically, are detectable by X-rays. Such foci of absorption, viz., areas of decreased density, frequently are located in regions subjected to _pressure_. Thus they may occur at the inner surfaces of the heads of the first metatarsal bones, or they may form underneath large tophaceous deposits in the soft tissues.