The primary state of all the tissues of the plant is the condition of simple cells, each of which is, in a certain sense, an independent body, having its own life-work and history in the complicated mass of which the tree is composed. All extension of the tree in any direction is made through the medium of cell-growth and cell-modifications, and, wherever there is cellular tissue in a state of vitality, there may be cell-multiplication whenever material for growth, i. e., sap in different stages, is brought into contact with such tissue.
In the case of the pine-stumps alluded to, the medullary rays of the recent wood retain their vitality, and, when the sap rises, it is transmitted through these rays and through the interspaces of the woody matter to the surface beneath the bark, these being appropriated to the organization of new cells whose walls are thickened by continuous secondary deposits, as in the normal formation of woody tissue. Of course, the amount of this woody formation will be limited, from the deficient supply of sap and want of concentration which it would obtain by passing through the leaves.
Puncturing the Pericardium.—The pericardium, or membranous sac surrounding the heart, sometimes becomes so filled with liquid that the movements of that organ are impeded. This is called dropsy of the heart. The surplus fluid may be relieved by the introduction of a trocar into the sac, but the operation is regarded as extra hazardous. Dr. Chairou, of the Paris Academy of Medicine, has tried a new method of treating the disorder in question. A young soldier just recovered from a pleurisy was found presenting all the symptoms of dropsy of the heart. The physician made a puncture into the pericardium with a capillary needle, and sucked out a considerable quantity of thick sero-sanguineous liquid, which soon became coagulated. The following morning the patient was pacing the corridors of the hospital in the very best of spirits.
Slag as a Building-Material.—"What shall be done with the slag?" is always a very urgent question for the proprietors of iron-works. Many are the plans which have been proposed for the utilization of this waste material, but, if we are to judge of their value by the amount of slag utilized, it must be confessed that they do not help to answer the iron-manufacturers' question. And yet many of the processes for the conversion of slag into a material for building would seem to promise very fair results. Mr. S. Egleston lately read a paper before the American Institute of Mining Engineers, in which he gives a history of these processes, stating at the same time, in a few words, the salient peculiarities of each. After recounting the failures which attended the first efforts, the writer sets forth the process followed in Königshütte, Silesia. There the slag is run from the furnace into a hemispherical basin on wheels, the bottom being strewed with sand or fine coke-dust to the depth of an inch. It is then drawn to the place where it is moulded into bricks. The slag and sand having been mixed together till most of the gases have escaped, the whole is pressed into a mould, and punctured frequently to let out the gas. A close-fitting cover then compresses it. The red-hot brick is next taken to the kiln, covered with powdered coal, and left to anneal. Four men make 500 bricks in five hours. In Silesia these bricks cost 25 per cent, less than ordinary bricks. The lead-slag of the furnaces in the Hartz Gebirge gives bricks of inferior quality, being very brittle. A Belgian engineer, M. Sepulchre, was the first to successfully transform slag into a stone which could be generally used. He caused the slag-channels to terminate in an excavation, the sides of which had an inclination of 30°. This steep inclination causes the section of the pits to increase very rapidly, allowing the solid crust on the surface of the liquid slag to rise with it without being attached. The mass takes from five to ten days to cool. The product is a stone which, rather soft at first, grows hard on exposure to air. Slag suitable for such treatment should contain from 38 to 44 per cent. of silica. Experiment shows that stone of this kind made from the slag coming from white iron can bear a pressure of 242 kilogrammes (500 pounds) to the square centimetre (one-third of an inch) without fissure. If from gray iron, it will not crush at a pressure of 405 kilogrammes. It is, therefore, stronger than the best marble.
