Page:Popular Science Monthly Volume 40.djvu/443

Rh gives an antiquity of not more than ten thousand years to the end of the Glacial epoch—a conclusion supported by the enlargement of post-glacial valleys and the silting up of small post-glacial lakes.

Determination and Cultivation of Bacteria.—Many scores of bacteria, says Prof. John B. Roberts, in an address on the Relation of Bacteria to Practical Surgery, have been, by patient study, differentiated from their fellows, and given distinctive names. Their nomenclature corresponds in classification and arrangement with the nomenclature adopted in different departments of botany. Thus we have the pus-causing chain-coccus (Streptococcus pyogenes), so called because it is globular in shape; because it grows with the individual plants attached to each other, or arranged in a row, like a chain of beads on a string; and because it produces pus. In a similar way we have the pus. causing grape-coccus of a golden color (Staphylococcus pyogenes aureus). It grows with the individual plants arranged somewhat after the manner of a bunch of grapes, and, when millions of them are collected together, the mass has a golden-yellow hue. The difficulty of investigating these minute forms becomes apparent when it is remembered that under the microscope many of them are identical in appearance, and it is only by observing their growth when they are in a proper soil that they can be distinguished from one another. In certain cases it is difficult to distinguish them by the physical appearance produced during their growth. Then it is only after an animal has been inoculated with them that the individual parasite can be accurately recognized and called by name. It is known, then, by the results which it is capable of producing. Bacteria may also be distinguished by their individual peculiarities of taking certain dyes. The similarity between bacteria and ordinary plants with which florists are familiar is remarkable. Bacteria grow in animal and other albuminous fluids; but it is as essential to them to have a suitable soil as it is for the corn or wheat that the farmer plants in his field. By altering the character of the albuminous fluid in which the microorganism finds its subsistence, these small plants may be given a vigorous growth, or may be starved to death. The farmer knows that it is impossible for him to grow the same crop year after year in the same field, and he is, therefore, compelled to rotate his crops. So it is with the microscopic plants which we are considering. After a time the culture-field or soil becomes so exhausted of its needed constituents, by the immense number of plants living in it, that it is unfit for their life or development. Then this particular form will no longer thrive; but some other form of bacteria may find in it the properties required for functional activity and may grow vigorously. Again, there are certain bacteria which are so antagonistic to each other that it is impossible to make them grow in company or coexist in the blood of the same individual. An animal inoculated with erysipelas germs can not be successfully inoculated immediately afterward with the germs of malignant pustule. As the horticulturist is able to alter the character of his plants by changing the circumstances under which they live, so can the bacteriologist change the vital properties and activities of bacteria by chemical and other manipulations of the culture-substances in which these organisms grow. The power of bacteria to cause pathological changes may thus be weakened and attenuated; in other words, their functional power for evil is taken from them by alterations in the soil, and vice versa.

Properties of Peroxide of Hydrogen.—Peroxide of hydrogen has been a subject of experiment by Dr. B. W. Richardson, chiefly with regard to its medical uses, for more than thirty years. He regards it as a solution—although it may be made to take on the gaseous form—and as consisting of water containing, according to strength, so many atmospheres of oxygen; or as an oxygen atmosphere in solution. It is not, however, a mere mixture, but a peculiar chemical compound. The oxygen can be made to accumulate, volume by volume, until the volume of water can rise to ten, twenty, thirty, and some say even more than a hundred volumes of oxygen, before complete saturation is reached and a volatile body is formed. The combination of the added oxygen in hydrogen peroxide is stable in the presence of some substances, unstable and easily evolved in the