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figure at B E, which carried almoft all the blood from A B, through 

 B E, into the vein D E F, in which vein the blood was conveyed 

 from E to D, and all the blood which lay between E F was coa- 

 gulated. 



When thofe Perch which I examined were very lively, and their 

 tails unhurt, I could not difcern the large veflels in their tail fins, 

 but when the blood began to coagulate, fome of the veflels, in a 

 fliort time, appeared fifty times larger than their natural fize. There 

 were other vellels in which the blood had circulated, and were not 

 fwelled, but here the blood was at a fland, and the veflels them- 

 felves, by reafon of their minvitenefs and there being no circulation, 

 in them, were not eafily difcerned. 



Moreover, it was my opinion that many of the large circulations 

 of the blood, which I faw, when it began to flagnate, were not 

 performed within the coats of the blood- vellels, but that, when the 

 blood in the arteries was impeded in its courfe, the continued and 

 ftrong propulfion from the heart caufed it to form new canals, where 

 the fifli's fkin made the leafl refiftance, and that it was by this 

 means the oblique current of blood, fliewn in Jig. 14, at EB, was 

 formed. And, indeed, I am of opinion that all thofe very minute 

 currents, whether we call them arteries or veins, are not performed 

 within the coats of veflels, but that they are formed where the blood, 

 in its protrufion from the heart, meets the leafl refinance. But if 

 we fuppofe one of the very fmallefl blood-veffels to be provided with 

 a coat, and fuch coat to confift of three ditlinft membranes, as it is 

 faid the coats of the veins and arteries are formed, it neceffarily fol- 

 lows that the coats of thofe minuteft vefTels muft be of a thinnefs 

 which is inconceivable. For, let us fuppofe, as I have often faid, 

 that the axis of an hundred globules of the blood, from whence its 

 rednefs proceeds, are no more than equal to the axis or diameter of 

 a large grain of fand; it follows, that ten thoufand globules of blood 

 may pafs together through a veflel, no larger than to admit a large 

 grain of fand to pafs through it. Now, fuppofing the coat of fuch 



