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grains, yet the part wliercin the blood-vefTels were feen, did not 

 amount to a fourth of that fpace ; fo that, within lefs corapafs than 

 that of a grain of fand, there are found to be in the tail of an eel, as 

 great a number of blood-veflels as are here re])refented between 

 1,2,3,4. 



At the letter A, is reprefented one of thofe blood-veflels. which 

 are called veins ; B, one of thofe named arteries ; C, is a vein ; D, 

 an artery ; E, another vein, and F, another artery. 



But, in order more clearly to explain the courfe of the blood in 

 thefe veflels, and to fhew, at what part, though in fa6l they are one 

 and the fame, they aiTume different names, 1 have in the figure more 

 particularly pointed out, and fliall now defcribe one of thole veflels 

 called an artery. 



D, is that artery, out of which, at G, proceeds a fmall branch, 

 which, at H, divides itfelf into two, as HIK: and here we fee, that 

 the branch GH I is properly to be named an artery, becaufe, as far 

 as I, the blood is driven from the heart, and IK, we muft name a 

 vein, becaufe, from I to K the blood is brought back towards the 

 heart. In the other branch, which proceeds from H, in the dire61ion 

 H LM, the blood is infufed into the vein E at M; and fince at M it 

 firft begins to take its courfe towards tlie heart, it follov,s that at M 

 this veffel lirft alTumes the name of a vein. 



In this fmall artery G H, it is to be obferved that the limner has 

 been very accurate in defcribing the exv.61 fize of the veflel, and we 

 mufl: always bear in mind, that in thefe branchings, or ramifications, 

 the arteries grow fmaller and fmaller, and the veins continually grow 

 larger, as they receive the blood from the arteries. Farther, all the 

 minute blood-veflels defcribed in this figure the limner has repre- 

 fented, not by lines, but by fmall circular dots, fo as to give an idea 

 of the particles or globules of blood, which he very dillinftly faw, 

 running or paffing through them. 



All the minute veflels which are reprefented in this figure, of the 



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