CHEMICAL CHARACTERISTICS OF THE TOPHI IN GOUT.
Scheele in 1776, Tennant and Pearson in 1796, and Wollaston in 1797, demonstrated the existence of uric acid in the concretions of gout. Since then, a number of analyses have been made by physio logical chemists. The results obtained by Laugier, Wurzel., and Lehmann are given in the following table : Lehmann's specimen was taken from a metatarsal tophus, and it is probable that it included a fragment of bony substance. When an unmixed specimen can be obtained, it usually consists almost exclu sively of the salts of uric acid. These can be easily recognized by the following reaction: 1. Treated with dilute hydrochloric acid there is no effervescent escape of carbonic acid gas; consequently calcium carbonate is not present.
2. Treated with nitric acid the tophus dissolves. The solution should be evaporated in a porcelain capsule to one-third its volume, when, if uric acid be present, a yellowish deposit appears, and, on addition of a few drops of ammonia, exhibits a rich purple color.
This is known as the murexid test, and it affords a very accurate method of demonstrating the presence of uric acid.
3. If a tophaceous fragment be calcined in a capsule, the pres ence of animal matter will be indicated by the characteristic odor. Treating the alkaline residuum with a solution of silver nitrate, the abundant precipitate of silver chloride testifies to the presence of chlorides, which may be further shown to be in combination with sodium.
4. If a preparation be placed under the microscope and treated with a drop of acetic acid, it is possible to view the solution of the urate of sodium, and the precipitation of uric acid crystals upon the surface of the glass slide.
By these tests it is always possible to distinguish a uratic deposit from masses of merely calcified tissue. In the examination of abar ticular and visceral lesions, this discrimination sometimes becomes a matter of importance, as will become evident in the study of the