Sentence:  ... comparatively speaking, few are convinced of, or perhaps acquainted with the fact, that not only do the "bed-clothes" intercept and retain a large proportion of this <WSD>offthrow</WSD>, but that it penetrates both beds and mattresses, which actually absorb a large proprtion of it, ... 
Meaning of the word marked with <WSD> tags:  That which is thrown off (i.e. discarded, ejected, or emitted)