This section is from the book "The Transmission Of Life. Counsels On The Nature And Hygiene Of The Masculine Function", by George H. Napheys. Also available from Amazon: The Transmission of Life.
The differences of the sexes, the emotions which depend upon these differences, and the institution of marriage are primarily and directly existent for the purpose of transmitting life, or, to put it more plainly, for having children. Every married couple must distinctly and constantly impress this truth upon their minds, and be governed by it in their life. "Whatever relations they bear to each other, whatever duties they may have to society and themselves, all of them are subordinate to the paramount obligation of having and raising a family. We care not what excuse may be imagined in order to escape this duty, it is inadmissible. Nothing short of positive incapacity can exculpate either party.
It is not only their duty to have, not merely a child or two, but a family of children; but also, to do all in their power that their offspring have all the natural advantages which it is possible to give them. It may not be generally known that this matter touches some of the most intimate and earliest relations of the married couple. But, now-a-days, physicians at least are fully satisfied that the season and manner of conception, the condition of father and mother at the time, and several attending circumstances exercise a most important influence on the newly formed being. In order that this topic, which we believe to be one of the highest interest to all, may be properly understood, we are obliged to depart from the rule we have generally laid down for ourselves - not to trespass on the domain of the physiologist - and give a brief explanation, so far as that is possible with the present possessions of science, of that most mysterious and wonderful phenomenon, conception.