( 55 ) 
III. An Extract of a Letter from Mr. Anthony van Leeu- 
wenhoeck, F.R.S Dated Odober the nth. 1713- Concerning 
the Fibres of the Mifcles, &C. 
Gentlemen, 
I N compliance with your defires, I here fend you a Copy 
of the Obfervations 1 communicated to the great Penfio- 
nary Monfieur Heinfius, concerning the Membranes with which 
the Fibrill# of the Mufcles appear to be encom palled, both in 
the Fleih of a Whale, Cod-filh, Salmon, and Smelt ; and alfo 
in that from an Oxe to a Moufe ; in all which the appearance 
was the fame. 
The Flefh of the Whale, was a fmall piece cut off near the 
Tail of the Filh, which ! defired a Sea-Captain to bring me. 
that I might obferve how the Flefh in that part was joined to 
the Tendons in fo large an Animal. Viewing this thro’ the 
Microfcope, I judged the Fibres thereof to be four times as 
large as thofe I had formerly oblerved in another piece of 
Whale’s Flefh, taken from another part #f the Filh; which 
made me confider, whether the Fibres of that part might not be, 
by Nature, furnilhed with larger Fibres for its greater ftrength. 
Cutting the faid Flelh-parts length-wife, and a crofs the Fi- 
bres, I dilcovered more plainly than before, that each Particle 
or Flelh-fibre, was enwrapt in a fine thin Membrane. 
To have a better Idea of thefe Flefh-fibres of a Whale, I cut 
a thin (lice of it a-crofs, which I laid on a wetted piece of 
Glafs, that the Flefh which was very dry and Ihrunk, might, 
by the moifture be fwelled, and thereby diftended to the natu- 
tural fize it had when on the Body of the Filh itfelf. In this 
ftate, placed before the Microfcope, it appeared as I caufed it to 
be drawn in the Figure. A. B. C. D. in which the Parts were fo 
clofe together, that their encompafting Membranes, reprefented 
by the black Lines, were but juft difcernable, fome whereof 
appeared larger than others : thefe, if attentively viewed, feem’d 
I plainly 
