Page:Popular Science Monthly Volume 41.djvu/139

Rh argument. The bacteria are classified at once as "the lowest members of the vegetable kingdom, closely related to the algæ."

Separate species are found among them, differentiated by growth and shape. According to their forms they are divided into the globular bacteria or micrococci, the rodshaped or bacilli, and the screw-like or spirilla. Their structure, multiplication, conditions necessary for growth, and resultant phenomena are next considered.

The benefits of oil immersion and of the Abbe illuminating apparatus are unfolded in Methods of Investigation, and the learner is instructed in the handling of the microscope and making of stains. Even the common errors of beginners are outlined for the student, and he is warned not to mistake the broken nuclei of white blood-cells for bacilli, when the glasses have been too hastily pulled apart, or to fancy he has discovered a colony of micrococci when some plasma-cells betray idiosyncrasies in absorbing aniline colors.

Full directions are given for the various processes involved in successful breeding, sterilization, and the preparation of liquid and solid food media.

The noxious character of pathogenic bacteria is shown to consist not in the mechanical effect of their presence, nor in the hospitality they may exact from their host, but in the alkaloidal poisons they generate. Fraenkel inclines to the belief that the organism resists through a germ-killing power which resides in the living albumin of the serum, and that victory over invading bacilli is a chemical one and not the pitched battle of the phayocytes. Some of the interesting experiments of Metschnikoff in defense of his theory are not quoted, but his views are fairly represented. The author admits as pathogenic bacteria only those which comply with three conditions: first, that they are invariably present with the morbid affection; second, that they can be cultivated outside of the organism; thirdly, when the same pathological effects follow inoculation of the artificial culture. Petri's method of finding the number of bacteria in a given quantity of air is preferred. Only three to five germs in a litre is the average amount computed for an ordinary dwelling. Bacteriological examination of the soil is complicated and of little use, but that of water is extremely important, although the determination of species is difficult. "Water may be harmless and contain five thousand germs of the hay bacillus to the cubic centimetre, but ten germs among which are two cholera vibrios and two typhoid bacilli render it dangerous."

The principal mold and yeast fungi are briefly noticed in the appendix. The book is indexed, but lacks illustrations. Minute descriptions atone for this; however, the student is expected to illustrate for himself in the best way by observation of the living object.

electric traction in the United States only dates from 1884, its development has been so rapid that for public transit in towns and cities it would seem that the days of the horse are numbered. Of electric locomotion as a science and art this book is a clear and thorough presentation. Beginning with an outline of electrical theory, the authors proceed at once to practical details. The considerations which should determine the placing of a station are first discussed, as also the economical adaptation of plant to a specific volume of traffic and frequency of service. Steam-engines and water-wheels of the best models are described and their merits carefully discriminated. Motors and car equipment are then canvassed, and the various approved methods of building lines and track are illustrated. The trolley, underground conduit, and storage-battery systems are next compared, with a complete array of evidence pro and con.

Mr. Crosby, one of the authors, has conducted the only series of experiments ever undertaken with intent to double railroad speeds. In one of the most interesting chapters in the book he gives all the facts in the case, with cautiously deduced estimates. His conclusion is, that with electric motors of the highest efficiency, there is an advantage over the locomotive at all speeds. This advantage is fifteen per cent at twenty miles an hour, and steadily increases as the rate is quickened. Where motors are liable to a