Dr. Marie C. Stopes, Married Love: A New Contribution to the Solution of Sex Difficulties. Eugenics Publishing Company. Original 1918. Reprinted 1927 and 1931.
Dr. Snopes is very poetical doctor, with a solution to the problems of married love that I doubt that many would be willing to follow. She is in some ways a practical and reasonable woman, supporting the use of contraception, p. 112, and recommending that man and wife have some space for themselves, p. 96-99. However, she really gets carried away with what delicate flowers women are. Take for example:
"Welling up in her are the wonderful tides, scented and enriched by the myriad experiences of the human race from its ancient days of leisure and flower-wreathed love making, urging her to transports and to self-expressions, were the man but ready to take the first step in the initiative or to recognize and welcome it in her." P. 28.
"The sensitive interrelation between a woman's breasts and the rest of her sex-life is not only a bodily thrill, but there is a world of poetic beauty in the longing of a loving woman for the unconceived child which melts in mists of tenderness toward her lover, the soft touch of whose lips can thus rouse her mingled joy." P. 29.
Not surprising then, that her solutions for the problems that arise in marital relations are to have less or them. A lot less. Like about maybe for a day or three once a month:
"My law of Periodicity of desire in women it is possible to represent graphically as a curved line; a succession of crests and hollows as in all wave-lines. Its simplest and most fundamental expression, however, is generally immensely complicated by other stimulations which may bring into it diverse series of waves, or irregular wavecrests. ... Woman is so sensitive and responsive an instrument, and so liable in our modern civilized world to be influenced by innumerable sets of stimuli, that it is perhaps scarcely surprising that the deep, underlying waves of her primitive sex tides have been obscured and entangled so that their regular sequence has been masked in the choppy turmoil of her sea, and teir existence has been largely unsuspected, and apparently quite unstudied." P. 42-43.
"If this is put in the simplest way, one may say that there are fortnightly periods of desire, arranged so that one period comes always just before each menstrual flow. According to her vitality at the time, and the general health of the woman, the length of each desire period, or, as we might say, the size and complexity of each wavecrest, depends. Sometimes for the whole of as much as, or even more than, three days, she may be ardently and quite naturally stimulated, while at another time the same woman, if she is tired and overworked, may be conscious of desire for only a few hours, or even less." P. 47.
She does recognize exceptions for special occasions, though "If the man plays the part of the tender wooer, even at times when her passion would not spontaneously arise, a woman can generally be stirred so fundamentally as to give a passionate return. P. 64.
Moreover, this relative lack should be of no problem to the husband:
"Of what does this loss consist? It is estimated that there are somewhere between two and five hundred million sperms in a single average ejaculation. Each single one of these (in healthy men) is capable of fertilizing a woman's egg cell and giving rise to a new human being. (Thus, by a single ejaculation, one man might fertilize nearly all the marriageable women in the world. Each single one of these minute sperms carries countless hereditary traits, and each consists very largely of nuclear plasm -- the most highly specialized and richest substance in our bodies. This analysis of the chemical nature of the ejaculated fluid reveals among other things a remarkably high percentage of calcium and phosphoric acid -- both precious substances in our organization. It is therefore the greatest mistake to imagine that the semen is something to be got rid of frequently -- all the vital energy and nerve-force involved in its ejaculation and the precious chemical substances which go to its composition can be better utilized by being transformed into other creative work on most days of the month. And so mystic and wonderful are the chemical transformations going on in our bodies that the brain can often set this alchemy in motion, particularly if the brain is helped by knowledge. A strong will can often calm the nerves which regulate the blood-supply, and order the distended veins of the penis to retract and subside without wasting the semen in an ejaculation. But while it is good that a man should be able to do this often, it is not good to try to do it always. The very restraint which adds to a man's strength up to a point, taxes his strength when carried beyond it. It is my belief that just sufficient restraint to carry him through the ebbtides of his wife's sexual rhythm is usually the right amount to give the best strength, vigour and joy to a man if both are normal people. If the wife has, as I think the majority of healthy, well-fed young women will be found to have, a fortnightly consciousness or unconscious potentiality of desire, then the two should find a perfect mutual adjustment in having fortnightly unions; for this need not be confined to only a single union on such occasion. Many men, who can well practice restraint for twelve or fourteen days, will find that one union only will not then thoroughly satisfy them; and if they have the good fortune to have healthy wives, they will find that the latter, too, have the desire for several unions in the course of a day or two." P. 59.
And if the denial prescribed so far is not enough, she thinks that to be safe, a married couple should refrain from sex for the last six months of pregnancy. P. 117. She will allow it if the wife wants it, however, based, apparently on the scientific conclusion that children whose mothers wanted sex during pregnancy and were denied it had children that grew up restless, uncontrollable, and with a marked tendency to self-abuse. P. 118.