Formerly it was thought that the vital point of time was fertilisation, the fusior of spermatozoon and ovum, but it is now realised (although the point as not come before the courts) that this position is not maintainable, and that conception for legal purposes must be dated at earliest from implantation.

The legislation is unspecific. The abortion section does not expressly refer to conception; it speaks merely of a "miscarriage." There is, therefore, nothing to prevent the courts interpreting the word "miscarriage" in a way that takes account of customary and approved birth control practices.

After fertilization the human egg stays in the uterine tube for three days, then descends to the uterus and on about the 10th day after fertilization attaches itself to the uterine wall . ("implantation" or "nidation"). The widely-used method of birth control called the intrauterine contraceptive device (IUD), such as the coil or loop, works by destroying the blastocyst (the developing egg) or preventing it from implanting itself. If, therefore, conception refers to fertilization, the' IUD should be named post-conceptive rather than contraceptive. So-called oral contraceptives may also act in this way, for as well as suppressing ovulation there is evidence that they can prevent the fertilized ovum implanting or for long remaining implanted. That is certainly the mechanism of post-coital oestrogen and progesteron administration, these substances (the so-called "morning after" pill) being effective if used within 72 hours of coitus.91f these methods of birth control are abortifacient they are illegal, unless administered by a doctor with the specified opinions of two doctors and in a hospital or registered nursing home under the Abortion Act. But no one who uses or fits IUDs supposes that they are illegal or are governed by the Abortion Act.

The only way to uphold the legality of present medical practice, to make IUDs contraceptives and not abortifacients, is to say that for legal purposes conception is not complete until implantation. An advisory group established by the British Council of Churches took this line. Moreover, it has been accepted by the Department of Health and Social Security, and the Attorney­ General has decided that pills designed to inhibit implantation are not abortifacient and their use is not criminal. The legal argument is that the word "miscarriage" in the abortion section means the miscarriage of an implanted blastocyst.

The line of argument would uphold the legality of a universal medical practice, and would therefore provide a partial solution to immediate problems. But our birth control methods have a devastating effect upon the anti-abortionist argument that there is something magical or divine about the moment of fertilization which brings about a new "human person" whc must be fully protected by law. If all abortion is a kind of murder, it must be recognised, ir the words of Dr Colin Brewer, that uncounted thousands of human beings are slaughtered each day by widely accepted birth control devices, as well as by the pill. Those who an unwilling to denounce these forms of birth control cannot consistently argue for the prohibition of abortion from the moment of fertilization.

Even dating the prohibition of abortion from implantation does not establish the legalit" of the gel and prostaglandin preparations, now being developed, which expel the fetus at a early stage after implantation. There is an argument for interpreting the word "miscarriage to allow still a little more leeway on this question. "Miscarriage" may be interpreted to mea the miscarriage of a fetus when it has achieved a certain degree of recognisable huma organisation. In particular, those whose objection to abortion depends upon belief in the SOl may be impressed by the fact that until two weeks after conception it remains uncertai whether the egg will become twins (or quins) instead of a single person. Since theology h: never contemplated the division of the soul, this implies that the soul cannot enter the boc for at least a fortnight after conception. So this argument takes us back to "media animation."