Page:Popular Science Monthly Volume 19.djvu/724

706 carried out, will not be far greater in the long-run than its benefits.

The many American friends of Mr. Herbert Spencer will be pleased to learn that he contemplates visiting this country next year. He has long wished to do so, but has been deterred from seriously thinking about it by the state of his health, which forbade the venture of an Atlantic voyage. But he is now so much better that this difficulty is removed, and he hopes to come over some time next summer.



readers of "The Popular Science Monthly" have been from time to time informed concerning the progress of inquiry in relation to those lowest, minute, and curious organisms now known under the general name of "Bacteria." The first observer who perceived them was the father of microscopy, the Dutchman Leuwenhoek, as early as 1675. He was examining with his magnifying-glasses a drop of putrid water, when he remarked with profound astonishment that it contained a multitude of little globules which moved with agility. In 1773 they were studied by O. F. Müller, and classified as a group of the Infusoria. They soon began to occupy a good deal of the attention of microscopists, and there was much conflict of opinion about their nature, as was inevitable from the novelty of the research and the imperfection of instruments. At one time they were considered as animals, and at another they were taken for plants; were now ranked as Algæ, and again as fungi. But it is only in the present generation that our knowledge of them has become so perfect as to lead to a large amount of agreement among observers respecting their nature, varieties, and classification. It is now recognized that they are the lowest organisms, standing upon the limit of the two kingdoms, animal and vegetable, and are thus defined by the botanists who have most recently studied them: Cells deprived of chlorophyl, of globular, oblong, or cylindrical form, sometimes sinuous and twisted, reproducing themselves exclusively by transverse division, living isolated or in cellular families, and having affinities which approach them to the Algæ, and especially to the Oscillatoriæ. There has been, as our readers are aware, a long and intense struggle over the question of their spontaneous generation, but the great preponderance of opinion is now against that mode of origin. They vary much in form and dimensions, but are regarded as the smallest of all microscopical beings. Some of them are motionless, but they are generally remarkable for the movements they exhibit. These are thus described by the eminent observer Cohn:

In certain conditions they are excessively mobile; and, when they swarm in a drop of water, they present an attractive spectacle, similar to that of a swarm of gnats, or an ant-hill. The bacteria advance, swimming, then retreat without turning about, or even describe circular lines. At one time they advance with the rapidity of an arrow, at another they turn upon themselves like a top; sometimes they remain motionless for a long time, and then dart off like a flash. The long rod bacteria twist their bodies in swimming, sometimes slowly, sometimes with address and agility, as if they tried to force for themselves a passage through obstacles. It is thus that the fish seeks its way through aquatic plants. They remain sometimes quiet, as if to repose an instant: suddenly the little rod commences to oscillate, and then to swim briskly backward, to again throw itself forward some instants after. All of these movements are accompanied by a second movement analogous to that of a screw which moves in a nut. When the vibrios, in the shape of a gimlet, turn rapidly round their axis, they produce a singular illusion: one would believe that they twisted like an eel, although they are extremely rigid.

An order of beings so amazingly minute that the various kinds of them are just barely revealed by the utmost powers of the microscope, might seem of little importance, at least, practically, in this world's concerns. But this is not so. The bacteria are at the foundations of life, and it is now admitted that they have a grand office in relation to the general preservation and continuance of life. Exactly in what way is perhaps not yet determined; but they are in some way 