Williams, W. L. (14), calls attention to the lack of veterinary literature relating to the pathology and bacteriology of the male genital tract, except as related to infection with _Bact. abortum_. Infection with other types of bacteria is emphasized, the clinical recognition of such, with the accompanying pathological changes, and of the numerous phenomena involved in the process of reproduction in the male. The semen and its essential germinal elements are taken up with reference to the entire lack of study devoted to them, and some of the abnormal changes are described. In a later contribution (15), he takes up the part played by the bull in the dissemination of genital infections and states: “Clinical studies now indicate with great clearness that the bull is an active spreader of that group of genital infections which cause sterility, abortion, and related phenomena.” Williams, W. W. (16), studied the semen with reference to sterility, emphasizing the importance of its examination in the diagnosis, giving methods for collecting samples, staining of sperms, and some of the abnormalities encountered. The work is fundamental, and should be of great practical importance to all interested in the problem. In a later paper (17), he brings out a more extended discussion of the question. He concludes that the clinical examination is of vital importance, and that the efficiency of the semen depends not only upon its physical properties but upon the number of spermatozoa that are motile, the degree of motility, degree of obligospermia, and the percentage of imperfect spermatozoa, either deformed or immature. Of forty bulls examined, he finds that twenty, or fifty per cent, showed lessened fertility, and others, aside from this, showed minor changes in the genital organs or semen. The same author subsequently takes up the subject of reproduction from the viewpoint of both sexes, but emphasizing infection in the male, and the frequency with which lowered vitality of the germinal cells occurs. Hopper (18) states: “A diseased bull may manifest non-fertility or decreased potency in different ways—by repeated service to apparently normal females without conception, by a high abortion rate in females that have been apparently normal, by characteristic infections following the use of any particular sire, or by abnormalities in the breeding tract noted by rectal or physical palpation.”