DISTINGUISHED AND ACCOMPLISHED SIR,--The arrival of your letter lately gave me the liveliest pleasure, and the receipt at the same time of your learned comments upon Lucretius satisfied me that you are not only living and well, but that you are at work among the sacred things of Apollo. I do indeed rejoice to see truly learned men everywhere illustrating the republic of letters, even in the present age, in which the crowd of foolish scribblers is scarcely less than the swarms of flies in the height of summer, and threatens with their crude and flimsy productions to stifle us as with smoke. Among other things that delighted me greatly in your book was that part where I see you ascribe plague almost to the same efficient cause as I do animal generation. Still it must be confessed that it is difficult to explain how the idea, or form, or vital principle should be transfused from the genitor to the genetrix, and from her transmitted to the conception or ovum, and thence to the fœtus, and in this produce not only an image of the genitor, or an external species, but also various peculiarities or accidents, such as disposition, vices, hereditary diseases, nævi or mother-marks, &c. All of these accidents must inhere in the geniture and semen, and accompany that specific thing, by whatever name you call it, from which an animal is not only produced, but by which it is afterwards governed, and to the end of its life preserved. As all this, I say, is not readily accounted for, so do I hold it scarcely less difficult to conceive how pestilence or leprosy should be communicated to a distance by contagion, by a zymotic element contained in woollen or linen things, household furniture, even the walls of a house, cement, rubbish, &c., as we find it stated in the fourteenth chapter of Leviticus. How, I ask, can contagion, long lurking in such things, leave them in fine, and after a long lapse of time produce its like in another body? Nor in one or two only, but in many, without respect of strength, sex, age, temperament, or mode of life, and with such violence that the evil can by no art be stayed or mitigated. Truly it does not seem less likely that form, or soul, or idea, whether this be held substantive or accidental, should be transferred to something else, whence an animal at length emerges, all as if it had been produced on purpose, and to a certain end, with foresight, intelligence, and divine art.