Page:Popular Science Monthly Volume 41.djvu/635

Rh blood of an infected animal. To-day no one questions the etiological relation of Bacillus anthracis to the disease anthrax. And this bacillus has served for innumerable experiments relating to the solution of a variety of questions in pathology and preventive medicine. Among these we may mention the following, each of which has an extended literature: attenuation of virulence; protective inoculation of susceptible animals; hereditary transmission of protection; passage of pathogenic bacteria through the placenta, from the mother to the fœtus; explanation of acquired immunity; comparative value of germicidal agents and of antiseptics; conditions governing spore formation, etc.

Proceeding with our historical review: In 1873, Obermeier, a German physician, announced the discovery, in the blood of patients suffering from relapsing fever, of a minute, spiral, actively motile micro-organism the—Spirochete Obermeieri—which is now generally recognized as the specific infectious agent in this disease. Recently (1890) a spirillum closely resembling the relapsing-fever spirillum has been discovered by Sakharoff, a Russian investigator, in the blood of geese. The investigations of the author named show that it is the cause of a fatal epidemic disease which occasionally prevails among geese in certain swampy localities in Caucasia.

In 1879 Hansen reported the discovery of bacilli in the cells of leprous tubercles. Subsequent researches have shown that this bacillus is constantly associated with leprosy, and presumably bears an etiological relation to the disease.

In the same year (1879) Neisser discovered the "gonococcus." The bacillus of typhoid fever was first observed by Eberth, and independently by Koch, in 1880, but it was not until 1884 that Gaffky's important researches relating to this bacillus were published. It is now well established that this bacillus is constantly found in the spleen and intestinal glands involved in cases of typhoid fever; and pathologists have generally accepted it as the specific etiological agent in this disease. We can scarcely doubt the correctness of this conclusion, although it must be admitted that no satisfactory experimental demonstration of the fact has yet been made, inasmuch as none of the lower animals are subject to the disease as it occurs in man, and inoculations with pure cultures do not give rise to identical morbid phenomena. Since the discovery of the typhoid bacillus very numerous researches have been made to determine in an exact manner its biological characters, its resistance to germicidal agents, the duration of its vitality in drinking-water and in the soil, its presence in water the ingestion of which has been suspected of causing typhoid fever in man, etc. As to the results of these investigations we may say, in brief, that it has been shown that the