It is important to know that there are other uses for the procreative element than the generation of physical offspring, far better uses than its waste in momentary pleasure. It may, indeed, be better wasted than employed in imposing unwelcome burdens on toilworn and outraged women. But there should be no waste. This element when retained in the system may be coined into new thoughts, perhaps new inventions, grand conceptions of the true, the beautiful, the useful; or into fresh emotions of joy, and impulses of kindness and blessing to all around. This is, in fact, but another department of procreation. It is the procreation of thoughts, ideas, feelings of good-will, intuitions of truth - that is, it is procreation on the mental and spiritual planes, instead of physical. It is just as really a part of the generative function as is the begetting of physical offspring. It is by far the greater part; for physical procreation can ordinarily be participated in but seldom; while mental and spiritual procreation may and should go on through all our earthly lives - yea, through all our immortal existence.
Isaac Newton, Source: Karezza Ethics of Marriage (Second Edition), Alice B. Stockham, M.D.. pg 99-100