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lary or marrowy fubftance of the Brain, proceeds from this, 

 tliat the greater part of it confifls of pellucid particles, which are 

 ■fo clofely joined together, that they exhibit a glafly or watery tranf- 

 parency, and that the dark colour is increafed by the multitude of 

 blood-veflels paffing through it. I alfo obferved many very minute 

 particles, which I judged to be globules, about the fixth part of the 

 fize of a globule of human blood : thefe were not tranfparent, and 

 gave the Brain a darkifli colour, and refpecling them I thought 

 that, perhaps, they might have iflued from fome of the blood-vellels 

 which I had cut afunder. 



We may alfo perceive that this corticle of the Brain is, in many 

 places, deeply mixed among the medullary parts, but w hen we come 

 to feparate them gently, we find, betw een the two, fo great a num- 

 ber of blood-vellels, that they feem to conftitute an entire mem- 

 brane ; and we Ihall find that this internal part has as many blood- 

 velfels as the corticle, or external part, of the Brain. Befides thefe 

 fmall blood-veflels, I obferved in the Brain other veflels fo flender 

 that, in my judgment, none of the before-mentioned globules, 

 though divided into a thoufand parts, could pafs through them. T 

 do not here take any notice of thofe blood-veflels as large or larger 

 than a hair of one's head, which in great numbers run among the 

 medullary parts of the Brain, and are every where again divided 

 into branches, 



When I came to what is called the medullary fubflance of the 

 Brain, I obferved feveral irregular globules of different fizes, fome 

 of which were equal to the fize of a globule of human blood, and 

 fome larger, and which, as well as I could judge by my eye, for 

 the mofl: part confifted of a thin, tranfparent, and oily fubfliance. 

 Thefe globules are formed in the medullary part of the Brain (and 

 principally in that part where the fpinal man-ow begins), in fuch 

 quantities that they feem to conftitute the greatefl part of the Brain. 

 This great multitude of tranfjparent globules caufes the white colour, 



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