Of the mufcular Fibres of Animals. 31 
microfcope, found the fibrils, and even the leaft tubuli. 
that compos’d them, filled and tinged with the fame, 
yet the fmall ramifications of the nerves appear’d per-. 
fe£lly white. Whence it appears, that the fmall tubes 
which form a fibril, are really hollow; and that the 
extremities of the capillary arteries open into them, 
and empty therein a part of their liquor, which is 
re-conveyed by the veins into the heart. 
In the' fpinal marrow of an ox, Mr. Leeuwenhoek 
tells us, he faw with great delight minute hollow vef- 
fels of an inconceivable finenefs, invefted with their mem¬ 
branes, and extending length-wife parallel to each other, 
make up their compofition. He did not only difcern 
their cavities, which he computed to be three times lefs 
than their diameters, but in fome perceived the orifices, 
as the holes in a prick’d paper are feen, when held againft 
the fun. This examination requires the utmoft dexte¬ 
rity. For after a thin ilice of the fpinal marrow is placed 
before the microfcope, in lefs than a minute’s time it be¬ 
comes dry, and the whole appearance loft *. 
He alfo examined the brain of an Indian hen, a 
Iheep, an ox, a fparrow, &c. and did in them diftin- 
guifh multitudes of veftels extreamly fmall j and farther 
t obferv’d, that the veftels in the brain of a fparrow 
are no fmaller than in an ox, and from thence he ar¬ 
gues, that there is no other real difference between the 
brain of a larger and a fmaller animal, but only a greater 
or a fmaller number of veftels ; and that the globules 
of the fluid pafting through them, are in both of the fame 
fize. 
9 Arc. Nat. Tom. iii. p. 310, 355, 440. * Ibid. Tom. i. 
Part i. p. 38. 
? . Of 
