The seminal product is derived from several sources. A part comes directly from the tes ticle, some is discharged from the vesicular serninales, and with the fluid from these sources is mixed at the time of emission a certain quantity of the product of the secre tion of the prostate body and Cowper's glands: but it is by no means well ascertained from which of these organs the two kinds of sub stance above alluded to are respectively de rived. The more fluid and milky portion is first ejected; the gluey or clear mucilaginous parts, frequently collected into small hard masses, are more abundant in the portion which is last emitted.
Several circumstances render it highly pro bable that a considerable quantity of the fluid emitted during sexual union is derived directly by secretion from the testicle. With a view to the illustration of this, De Graaf performed the experiment of tying the ducts of a dog immediately before coition, and found, on examining them afterwards, that they were much distended by the accumulation of semi nal fluid in the part of the vasa deferentia tervening between the ligature and the testicle. It may be remarked, however, there are no vesiculre seminales or reservoirs of semen in the dog, and the result of such an experiment can hardly with justice be applied to the human species. On the other hand, it may be re marked that in man, while the testicle con tinually secretes a small quantity of semen, and probably a larger quantity during venereal excitement, it is obvious that the vesiculm seminales serve as reservoirs in which the seminal fluid accumulates ; for when in the dead body fluids are thrown into the vas de ferens, they pass into the seminal vesicle of the same side and distend it before issuing by the orifice leading into the urethra. The se minal fluid after being secreted probably follows in the living body the same course; and from this circumstance as well as the suddenness of emission, it is reasonable to infer that the greater part of the ejaculated semen, though formed in the testicles, comes in man immediately from the seminal vesicles.
The seminal vesicles we may suppose then always to contain a certain quantity of seminal fluid in the state of health. The accumu lation of semen in these vesicles relieves the pressure which otherwise would distend too much the secretory and excretory ducts of the testicle, and the seminal vesicles are them selves relieved either by the sudden evacuation of their contents from time to time, or by the gradual absorption of the seminal fluid by the absorbents or bloodvessels.*
There is also reason to believe that the mucous lining of the seminal vesicles secretes a mucous fluid which is mixed with the prolific product of the testicles. In some animals, indeed, the vesiculm seminales open separately from the vasa deferentia and dis charge by their excretory duct a fluid peculiar to themselves.
The impotence caused by castration or by the ligature of the spermatic vessels suffici ently proves, that the testicles are the only source of that part of the emitted fluid upon which the fecundating power depends.
The properties of the fluid supposed to be derived from the prostatic body and Cowper's glands have not been satisfactorily examined.
The quantity of the seminal fluid emitted du ring sexual union varies in man from one to two or three drachms. The seminal vesicles are not, however, emptied at one emission, and, accord ing to Ilaller, when by repetition this comes to be the case, two or three days are required in man to fit them again for reproduction by a new supply of fluid.
Chemical properties of the spermatic fluid.— On cooling immediately after emission, the seminal fluid jellies slightly, but in twenty or twenty-five minutes it becomes more fluid than at first,—a change which does not appear to depend upon the absorption of moisture from the atmosphere, as its weight is diminished rather than increased.
The chemical properties of the seminal fluid have been examined in man and several ani mals. It is generally considerably heavier than water, has a peculiar odour, which in creases on keeping, is alcaline from the first, and gives off ammonia when heated. Left at rest for some time, it deposits crystals of phos phate of lime.
According to the analysis of Vauquelin human seminal I uid consists of the following ingredients : Water 90 Animal mucus Free soda 1 Phosphate of lime 3 Peculiar animal principle 100 In the spermatic fluid of the horse, Las saigne has detected, besides the above-men tioned ingredients, the following substances :— Muriates of potassa and soda, Phosphates of lime and magnesia, Peculiar animal matter called spermatine.