The amount of semen ejaculated at each coition is extremely variable; age, bodily development, previous abstinence or excess, exert a marked influence upon the quantity and the proportion of morphological ele ments, therefore upon the quality. Usually the amount varies between twenty minims to one and a half drachms. The production of seminal fluid, which is probably under the influence of the centre of the male sexual function, which lies in the lumbar portion of the spinal cord, be gins with the appearance of manhood, which occurs at about the same time as does puberty in the female. Until the thirteenth or fourteenth year the testicular secretion shows no spermatozoa, and for a short time after this only a few, which are undeveloped. After this the normal seminal production is established. In old age the seminal production is diminished and may entirely cease; there is no certain time at which this change occurs. In many weakly individuals or in those weakened by long-continued sickness, marasmus, or by sexual excesses, the sexual in stinct, the subjective manifestation of the testicular function, may be abolished early, while in other individuals the seminal production, in con tradistinction to the early and regular cessation of ovulation in women, as has already been proved (particularly by Casper, Dieu and Duplay, and in more recent times by Schlemmer), is preserved in old age. In the ejaculated semen, its characteristic elements, the spermatozoa, inny be seen in an active condition. Still the seminal production in old age is the exception. Duplay could detect normal semen in only seven of fifty one cases; in thirty not only was the number of spermatozoa lessened, but they were also altered in form; in fourteen, without any disease being' shown, no spermatozoa were to be recognized.
If the semen is subjected to a microscopical investigation, there is only one morphologically component part recognizable, the previously men tioned seminal bodies (seminal filaments, zoosperms, spermatozoa), which arise from the cells of the testicles, and which determine the male agent, wherever propagation occurs by the commingling of two generative ele ments. They exhibit very different forms in the different animal classes; bat in almost all classes it can be shown by great enlargement, but much more clearly by chemical reagents, that they consist of three parts, the head, central portion and tail, the origin of which from the spermatoblasts of the testicles we have just learned. In the human species, the head is the largest part; it is oval, slightly flattened; the central part is joined to the posterior part of the head, is much smaller than it, from which it is not sharply defined, and gradually grows smaller and passes over into the still smaller filiform tail part. It has been attempted to describe a particular structure in the interior of each part—in fact some have even claimed to have seen formations analogous to the abdominal organs, but this was soon shown to be a delusion. Still, a difference in the substance does exist, although it cannot be exactly shown. The length of a sper matozoon is about -5-1-8- of an inch; the length of the head is equal to yr of the total length, or about -th-o- of an inch. According to the investiga tions of Schlemmer, other component parts of the semen are: epithelial cells and roundish, granular formations, characterized by nuclei or fatty granules. Still, in the normal semen, the spermatozoa are in the major ity, as are for instance the red blood corpuscles in the blood, while the other formed elements are in the same proportion as are the colorless blood corpuscles in blood. As regards the chemical composition of the sperma tozoa, the investigation of the testicular substance of fishes, which con sists almost entirely of seminal elements, shows that they consist partly of an albuminous substance; they contain no mucin, but a considerable amount of protogon, lecithin or cerebrin. When reduced to ashes, the phosphates have principally disappeared.
The most marked peculiarity of these formations is their activity, which gives to them the appearance of living beings, and gave them the name of " Seminal animals." The power, which causes this locomotion, is peculiar to the protoplasm of many cells. The intensity of this power is very variable. In many classes it is hardly noticeable, in others it is only manifested by an amceboid change of form, and in others still it is very active and works a great change of locality of the whole spermatozoon.
The manner of movement is also very variable; in the human species it consists of to-and-fro motions of the tail from one side to the other, and which movement is passively participated in by the central portion, and which results in the change of locality of the whole spermatozoon. The rapidity with which half of such a movement of the tail is made with un diminished vitality, is estimated by Hensen to be one-quarter of a second. The change of locality hereby occasioned, so far as the direction is con cerned, is never a regular one; every spermatozoon moves forward exactly in that line to which the head is directed, so that the spermatozoa move about in the most varied way and in all directions. The direction is changed only when hindrances, such as epithelial cells, intervene. Often the obstacle is pushed to one side. According to Lott the forward move ment is at the rate of Jr of an inch per minute. Henle believes that a spermatozoon travels about I of an inch in from seven to eight minutes.
The power of movement of the spermatozoa is notably influenced by different conditions. A certain degree of dilution of the testicular secre tion, by the adinixtnre of the secretions of the previously mentioned glands, seems necessary, since the spermatozoa taken directly from the testicles show no movement, although they move about in the inferior di vision of the vas deferens. Perhaps the closeness with which the sperma tozoa are found in the testicles is the cause for the lack of movement. The duration of the power of movement of the spermatozoa, or, what perhaps amounts to the same thing, the duration of life, since with the cessation of movement, the destruction of the formation is inaugurated, at least its power of fructification is lost, is very variable. The spermato zoa may remain in the masculine sexual passages for months, without losing a particle of their vitality. They do not exist as long as this in the female sexual passages. While, according to different observations of the more highly organized animals, the spermatozoa are met with in a living condition in the various portions of the female genitals for eight days after their entrance (Bischoff, Pri.vost and Duma.s; in bees, the sperms is preserved in the seminal receptacle more than three years), in the human species they have only been traced as high as the cavity of the cervix, and living filaments have only been observed as late as the seventh day. (Hausmann.) The movements are much more difficult to preserve outside of the animal organism. Still, the movements only cease with the advent of putrefaction, consequently after one or two days. Of great importance in the study of sterility are those investigations into the influ ences exerted by different reagents upon the movements of the sperma tozoa. According to Mantegazza's investigations, the semen may be heated to 47° C. without arresting the movements of the spermatozoa; the temperature may also be lowered to 10° C. without impairment of their power of movement; in fact the cold seems to exert a conservative influence, since in semen treated in this way the spermatozoa showed signs of life six days afterward. If the spermatozoa are dried out through the abstraction of water by means of salts, the movements cease; by the addition of water, the power of movement is again restored. If too much water is added, the movements cease, only to be resumed upon the withAlrawal of the water. In general, water is detrimental to the semen; if the semen of animals is deposited in water, the movements of the spermatozoa cease usually in a few minutes, hut certainly in a few hours. Even the contact of the semen with urine is said to be detrimen tal; it is the same with those metallic salts to which the corrosive subli mate belongs (a solution of corrosive sublimate of a strength of Toloo is sufficient). Acids at first accelerate the movements, but then cause them to cease forever, and alkalies in weak solution have the power to accelerate the movements. Organic poisons and neutral salts are without any influence. Engelmann, who, next to KUHiker, has carried out the greatest number of investigations of this kind, has arrived. at the conclu sion that every agent which is in a condition to restore the regular form and size of the dried or swollen spermatozoon is capable of causing the movement of the same.