In any case, whatever be the exact nature of the nucleus, the urate of soda collects thereupon, the acicular crystals tending to assume the form of radiating needles. But the successive depositions not being of regular incidence, the surface of the crystals, in the intervals of quiescence, becomes covered by _mucin_, animal or earthy matter. Hence, the concretions display not only a _radiating_, but a _concentric_ or _laminated_ structure. The mucin acts as the “binding substance,” the crystals lying in its meshes, and, moreover, remaining as the framework of the concretion even after the crystals are dissolved out; in other words, the gouty tophus is made up of a blend of _crystalloids_ and _colloids_, evolved from solutions of the same character. The importance of recognising the true nature of this binding substance, _i.e._, mucin, merits a brief digression, in light of Ebstein’s view that local tissue _necrosis_ is a necessary antecedent to uratic deposition. Now, exhaustive studies of the histology of uratic deposits, both those experimentally induced and of spontaneous gouty origin, have been conducted by Freudweiler, His, Krause, and Rosenbach. All their results, according to Gideon Wells, “indicate that uric acid and urates excite some slight inflammatory reaction, cause a slight local necrosis, and seem to act as a weak tissue poison.” According to Rosenbach, however, this sequence is not invariable, inasmuch as he noted that such deposits may occur without inducing necrosis. More pertinently to our contention, however, is it that Krause’s experience seems to indicate that errors of interpretation were possible. Thus, he suggests that part of the material in the areas of uratic deposits merely constituted the _framework_ of a crystalline deposit, though such were currently regarded as _strands_ of _necrotic tissue_. But, to resume, tophi being blends of _crystalloids_ and _colloids_, we must recollect that the suspension capacity of _colloidal_ solutions for crystalloids is much superior to that of simple solutions, by reason of the fact that at the surface of each colloidal particle there exists a zone in which the crystalloids are much more closely aggregated than elsewhere, thus permitting more crystalloids to be dissolved in the solvent between the colloidal particles. But, be it noted, this same tendency to concentration of the crystalloids at the surface of the colloidal elements leads to the colloids acting as determinants of _precipitation_ when _crystalloids_ are in excess. Accordingly, when the crystalloids pass out of solution, they form crystals or precipitates intimately blended with the colloids. Thus, for example, when uric acid crystallises out of urine it carries with it the colloidal pigments. On the other hand, if the colloids are precipitated, the solvent capacity of the solution being consequently depreciated, the crystalloids are deposited in intimate relation with the colloids.