The day is past when the importance of colloid-chemistry to the worker in the abstract or applied branches of science needs emphasis. The endeavor of the pure chemist to reduce all substances to crystalloid form and from the knowledge of their behavior to resynthesize the phenomena of nature has been a good one, but the limitations of such a point of view have grown daily more apparent. It happens that nature has chosen the colloid form in which to show her face. Crystalloid behavior is the exception, colloid behavior the rule, in the cosmos. Whether we deal with the regions above the earth, as the color of sky, the formation of fogs, the precipitation of rain and snow, or with the earth itself in its muddied streams, its minerals and its soils, or with the molten materials that lie under the earth, the problems of colloid-chemistry are more to the fore than have ever been the crystalloid ones.