Page:Popular Science Monthly Volume 31.djvu/441

Rh caries until it has reached the pulp. The inflammation of the pulp is particularly violent and painful, because the tissue is so richly provided with blood-vessels and nerve-filaments. As the products of inflammation can not escape, they collect and work their way downward, where they produce the most painful inflammation of the roots and the periosteum. The chief object of the rational treatment of caries of the teeth consists in the removal of every particle of carious substance out of the diseased tooth and the protection of the sound dentine that has been exposed against external injurious influences by covering it with a fine substance which is not attacked by acids—gutta-percha, cement, or gold. Although the dentine is not as unchangeable as enamel, but manifests, by becoming firmer or softer, that it is not quite uninfluenced by tissue-changes, yet its caries is not an irritative process that the dentine takes an active part in, but a passive process, and consequently the removal of all diseased portions and the protection of the non-carious part of the tooth suffices to stay the morbid process completely.

Cooking by Steam.—Professor Behrend, of Hohenheim, has described his experiments on the changes produced in the albuminoid matter of various seeds and of potatoes by steaming under high pressure. In a preliminary experiment, the author found that the albuminoids of lupine-seeds underwent considerable decomposition by heating with water under pressure, and that the decomposition was greater as the duration of the heating and the temperature increased. He, therefore, set to work to investigate whether the albumen was dissolved as well as decomposed, and, if so, what the quantitative relations of these changes were in various seeds, and more especially in the raw starch material for the manufacture of alcohol. Yellow lupines, peas, Hungarian maize, dari (Sorghum tartarieum), and potatoes in separate lots, nine months dug and just dug, were experimented upon. When the determinations were made, the contents of the flasks, especially when they were very starchy, became viscid and tenacious, like glue, at from 70° to 100° C, and at 130° C. they were almost clear, limpid liquids, with just a few flecks floating about, while, as the heating was continued, the masses became continually darker, the brownness being more or less intense, according as the substance was richer or poorer in nitrogen. It is hence inferred that the brown coloration is the result of the decomposition of nitrogenous substances. In all cases an increase of the soluble nitrogen was observed, especially with lupines and peas. The nitrogenous matter of maize seems less soluble, and not so easily attacked as that of lupines and peas. From the fact that the chief difference observed, after six hours of heating, was in the amounts of the albuminoid dissolved, it was inferred that the solution of albuminoids precedes decomposition, and this was confirmed by subsequent experiment.

Geographical Conditions and Civilization.—Mr. H. J. Mackinder shows, in a paper on "The Scope and Methods of Geography," how the distribution of men, their social and political relations, and the elements of their civilization, are determined by factors of physical geography and of geology back of it. "Each successive chapter postulates what has gone before. The sequence of argument is unbroken. From the position of the obstacles and the course of the winds may be deduced the distribution of rain. From the form and distribution of the wrinkle slopes and from the distribution of the rainfall follows the distribution of the drainage system. The distribution of soils is mainly dependent on the rock-structure, and on a consideration of soil and climate follows the division of the world into natural regions based on vegetation." Certain conditions of climate and soil are needed for the aggregation of dense populations. A certain density of population seems necessary to the development of civilization. Again, comparatively undisturbed strata usually underlie wide plains, and wide plains seem specially favorable to the development of homogeneous races, like the Russians and the Chinese. Yet, again, the distribution of animal, vegetable, and mineral products has done much to determine the local characteristics of civilization. An interesting chapter of geography deals with the reaction of man on nature. Man alters his