Sixtus V. says here: (1) that eunuchs "who lack both testicles certainly and evidently cannot emit true semen"; (2) that "although eunuchs may perhaps produce a kind of liquid resembling semen, this is by no means fit for generation or marriage"; (3) therefore eunuchs are forbidden to marry. The effects of castration in the eunuch are: (_a_) that all spermatozoa are absent; (_b_) that, as a consequence of the absence of the testicles, the power of penetration is lost; (_c_) that, as another consequence, the _liquor seminis_, which normally is formed in the seminal vesicles, the prostate and other glands, is no longer secreted. The eunuch, then, is completely impotent, in the full sense of the term. Ferreres is of the opinion, erroneously, that eunuchs, as a rule, have the power of penetration and of emitting a _humor semini similis_, and that amputation of the penis is requisite to cause impotence in eunuchs. There are only five authentic cases of temporary apparent potence in eunuchs in modern medical records, and these are explicable as cases of erethism from waste-product intoxication. The canonists who hold that the vasectomized man is impotent interpret the words of Sixtus V. to fit their opinion, although the vasectomized man has all the sexual potency of the normal man except that his spermatozoa are occluded. The _potestas coeundi_ is not lost in any degree; neither he nor the woman is conscious of any change whatever. Only the microscope can tell that the spermatozoa are absent if the fact that he has been vasectomized is not told. Moreover, if vasectomy has been done by mere cutting without considerable resection, and especially if the vasa have been shut by ligation alone, no one can be certain that the occlusion is either certain or permanent. There is always doubt that the spermatozoa are present if the microscope is not used, and these canonists all disclaim the use of the microscope in such circumstances. The argument Ferreres uses, to the effect that the absence of spermatozoa is seriously injurious to the woman, is a supposition of his own arising from an erroneous notion of potency in the vasectomized. This absence is not injurious to her, but it is probably injurious to the vasectomized man because of the partial ejaculation. Onanism, which is different, is decidedly injurious to both the man and the woman.