There are two essential parts in the semen, the spermatozoa and the carrying liquid. The spermatozoa, which fructify the ovum, are formed in the testicle; the liquid, which is the essential vehicle of the spermatozoa, and without which the spermatozoa are inert and sterile, is secreted, except a few drops from the testicles, at the distal end of the vasa deferentia under the base of the bladder, in the seminal vesicles, the prostate gland, and Cowper's and Littré's glands. The semen is made up of 90 per cent. water and 10 per cent. solids, and in these solids is the nitrogenous base called spermin, which is produced by the interstitial cells of the testicles and the prostate gland. Ovarin, secreted from the ovaries, corresponds in the woman to spermin in the man. The ductless glands, and some that have ducts, produce secretions which sustain the tone of the blood-vessels and neutralize the toxins from waste substances while these are in the body before excretion. An excess of spermin or ovarin causes congestion of the cerebrum and cerebellum and the nerve centres there, with consequent sexual erethism. When there is a pathologic sexual erethism from an excess of spermin or ovarin, vasectomy, castration, spaying, or the menopause cuts off this excess and the erethism disappears. Sometimes the waste product toxins excite the patient when the spermin or ovarin has been eliminated, just as the excess of spermin or ovarin excites, and the neurotic disturbance or sexual erethism continues until compensation by other glands neutralizes the irritating substance. The testicles in man are by no means the sole organ of generation. There are at least seventeen distinct organs in the male generative system. The seminal vesicles with the prostate gland are as necessary in generation as the testicles, as their removal sterilizes the spermatozoa and prevents the formation of the liquid vehicle. Castration effects an atrophy of several parts of the generative tract, and an irremediable degeneration; vasectomy cuts off the spermatozoa but causes no atrophy or degeneration, and the condition is remediable. Dr. Edward Martin of Philadelphia found active living spermatozoa in a testicle that had been ligated off for twenty years.