_The biological test._--This is carried out in the same way as the biological test for blood. Dr. C. G. Farnum, who proposed this test, uses semen or testicular emulsion for antigen, injecting 5 to 10 c.c. into the peritoneal cavity of a rabbit at intervals of from two to six days, on five or eight occasions. The antiserum is diluted from twelve to eighteen times with normal saline, and the semen four to twenty-five times. Human antiserum gives a precipitin reaction with the watery extract of human seminal stain, but not with testicular emulsions of the bull, dog, or goat, or with human blood serum.[14] [14] _Journ. Amer. Med. Assoc._, 1901, p. 1721. =Can a Rape be committed by one man on a healthy, vigorous woman?=--The answer to the question will, to a great extent, depend on the relative strength of the conflicting parties. Every case of rape has to be judged on its own merits. In any case, the medical jurist has simply to state, from the examination of the parties, that sexual intercourse has taken place, leaving the jury to decide whether a rape or not has been perpetrated. A case is mentioned by Casper where a healthy, strong adult of twenty-five years old was violated by a single man. =Can a Woman be Violated during Sleep?=--By this is intended natural healthy sleep, and not that induced by narcotics. In natural sleep, rape is scarcely possible in a virgin, especially if the hymen be found recently ruptured, though it _may_ be possible in a woman accustomed to sexual intercourse. [Illustration: Fig. 21.--Photo-micrograph of human spermatozoa, × 1000. (R. J. M. Buchanan.)] =Can a Woman become Pregnant by an act of Rape?=--The answer to this question is most decidedly in the affirmative. It is not necessary for a woman to experience any sexual pleasure during connection in order that she may conceive. A woman may become pregnant if fresh semen be injected into the vagina with a glass syringe. =Signs of Rape in the Dead.=--In the case of a woman found dead, the question may arise as to her having been violated prior to death. The reply to the question is by no means easy. Severe injury to the genitals is a presumption in favour of rape, but cases are by no means rare in which men failing to accomplish coïtus have injured the parts with their fingers. The presence of spermatozoa in the vaginal mucus is good evidence of a recent coïtus, but is no direct evidence of a rape. Collateral evidence will in most cases decide the point. Physical Signs of Rape in Adult and in Child