The early precipitation out of the “Boettcherchen” crystals is very characteristic of oligospermia, and impotent semen. The theory here is that crystals do not precipitate out when a fluid is actively moving, but soon do so when the fluid is motionless. The sediment which normally makes up about two-thirds of the sample is usually decreased in abnormal samples. The semen itself should be observed for unusual viscosity or a thin watery condition. Clotting should occur readily after emission, but the clot soon liquefies to some extent, allowing the spermatozoa to become more active. This clotting is, of course, to protect the delicate sperms from the hostile secretions of the vagina. The presence of immature and deformed types of sperms represents some disturbance of spermatogenesis, but it is difficult to explain the significance of these forms. They are seldom seen in normal samples, and undoubtedly none are capable of producing impregnation. In the case of minor abnormalities of staining reactions, the sperms are probably deficient in nuclear material or otherwise altered so that probably they are incapable of reaching and uniting with the ovum. When impregnation does occur in these cases, weak offspring undoubtedly result in many instances. The work has by no means progressed to the point where one may, by an examination of the semen, determine the degree of impotency with great accuracy, or even whether the animal may be restored to sexual health by proper hygienic and therapeutic treatment. Relatively, the greater the changes in the semen and spermatozoa, the less the chances of impregnation. Infertility to any marked degree, is, however, usually accompanied by corresponding changes in the seminal fluid and its germinal elements. Examination of the semen is, and probably always will be, simply an aid in reaching a diagnosis. While abnormalities of the semen and spermatozoa are associated with sterility or infertility, it is unwise to lay too much emphasis upon this method of diagnosis alone, especially with regard to the making of a definite prognosis. When large numbers of abnormal spermatozoa are present in the semen, we are safe in saying that the animal is, at the time, of lowered degree of fertility. One should be very cautious, however, in foretelling how long the condition will last, or if the animal may in time be restored to full fertility. Sterility, due to organic disturbances, probably seldom yields to treatment, but when it is due to functional disorders resulting from defective diet or lack of exercise, the condition is frequently remedied by overcoming the cause. Lack of exercise and overfeeding seem to be etiological factors in a fair percentage of cases.