The soiling of the conjugal bed by the shameful manoeuvres to which we have made allusion, is mentioned for the first time in Genesis xxxviii. 6, and following verses; 'And it came to pass when he (Onan) went in unto his brother's wife, that he spilled it on the ground lest that he should give seed to his brother. And the thing which he did displeased the Lord; wherefore he slew him.'
    Hence the name of conjugal onanism.
    One cannot tell to what great extent this vice is practised except by observing its consequences, even among people who fear to commit the slightest sin, to such a degree is the public conscience perverted upon this point. Still many husbands know that nature often succeeds in rendering nugatory the most subtle calculations, and reconquers the rights which they have striven to frustrate. No matter; they persevere none the less, and by the force of habit they poison the most blissful moments of life, with no surety of averting the result that they fear.
    So, who knows if the infants, too often feeble and weazened, are not the fruit of these in themselves incomplete procreations, and disturbed by preoccupations foreign to the genesaic act?

Augustus K Gardner, The Conjugal Relationships as regards 
Personal Health & Hereditary Well-being, 1894