Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     Nor do the powers divine grudge any man
The fruits of his seed-sowing, so that never
He be called "father" by sweet children his,
And end his days in sterile love forever.
What many men suppose; and gloomily
They sprinkle the altars with abundant blood,
And make the high platforms odorous with burnt gifts,
To render big by plenteous seed their wives-
And plague in vain godheads and sacred lots.
For sterile are these men by seed too thick,
Or else by far too watery and thin.
Because the thin is powerless to cleave
Fast to the proper places, straightaway
It trickles from them, and, returned again,
Retires abortively. And then since seed
More gross and solid than will suit is spent
By some men, either it flies not forth amain
With spurt prolonged enough, or else it fails
To enter suitably the proper places,
Or, having entered, the seed is weakly mixed
With seed of the woman: harmonies of Venus
Are seen to matter vastly here; and some
Impregnate some more readily, and from some
Some women conceive more readily and become
Pregnant. And many women, sterile before
In several marriage-beds, have yet thereafter
Obtained the mates from whom they could conceive
The baby-boys, and with sweet progeny
Grow rich. And even for husbands (whose own wives,
Although of fertile wombs, have borne for them
No babies in the house) are also found
Concordant natures so that they at last
Can bulwark their old age with goodly sons.
A matter of great moment 'tis in truth,
That seeds may mingle readily with seeds
Suited for procreation, and that thick
Should mix with fluid seeds, with thick the fluid.
And in this business 'tis of some import
Upon what diet life is nourished:
For some foods thicken seeds within our members,
And others thin them out and waste away.
And in what modes the fond delight itself
Is carried on- this too importeth vastly.
For commonly 'tis thought that wives conceive
More readily in manner of wild-beasts,
After the custom of the four-foot breeds,
Because so postured, with the breasts beneath
And buttocks then upreared, the seeds can take
Their proper places. Nor is need the least
For wives to use the motions of blandishment;
For thus the woman hinders and resists
Her own conception, if too joyously
Herself she treats the Venus of the man
With haunches heaving, and with all her bosom
Now yielding like the billows of the sea-
Aye, from the ploughshare's even course and track
She throws the furrow, and from proper places
Deflects the spurt of seed. And courtesans
Are thuswise wont to move for their own ends,
To keep from pregnancy and lying in,
And all the while to render Venus more
A pleasure for the men- the which meseems
Our wives have never need of.