A man with invisible perspiration emanating from him. Colour stipple engraving by J. Pass after Dodd.

"In the annexed copper-plate engraving, I have endeavoured to shew the manner in which the insensible perspiration issues from the pores of the body, which can only be discerned by means of a lens; being of so volatile and subtle a quality, that it passes through our garments with the utmost ease, particularly if woollen; and it even ascends through the bed-clothes like a mist, in the greatest abundance when we are asleep, and the animal functions at rest. In this manner, nature, from all casual obftructions, endeavours to relieve herself …"--Sibly, loc. cit., p. 126