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Upon this fubje6l of crabs, although I have fufficiently exliibited 

 to the learned world, the circulation of the blood in various animals, 

 and have demonllrated that it is uniformly and regularly performed 

 after the fame manner in all, yet, as I have met with perfons who 

 did not hefitate to deny this to be the fadl, I will here relate my ob- 

 fervations on two fmall live crabs, about an inch in diameter ; and, 

 judging that the extremities of their two fmalleft, or hind feet, 

 which were very broad and thin, would be proper objedls to 

 difcover the circulation, I placed one of them before the micro- 

 fcope, and immediately faw an incredible number of particles 

 of blood, which appeared to be globules ; thefe, though not red, 

 were of a darker colour than the liquor they floated in, and they 

 were running along a blood veflei which might be called a vein, 

 with fuch fwiftnefs, and fo great was the number of particles, that 

 it could not ealily be conceived but by an eye-witnefs. In fa<ft, I 

 cannot compare the appearance of thefe round particles of blood to 

 any thing better than by fuppoling we were to look through a large 

 opening, or a window, at a' fall of fnow, violently agitated by the 

 wind ; nor do I remember that I ever faw the blood driven through 

 the veflels with fuch fwiftnefs. It was alfo a moft delightful obje6l to 

 behold this large blood veflel, on each fide of it, crofl'ed by fmaller 

 veflels, in which the blood was driven forward with equal fwiftnefs. 



Upon changing the point, or place of view, I there faw the 

 blood in equal agitation, and in no lefs a number of veflels. 



Moreover, I happened to fee a veflel in which the blood could 

 not proceed in its regular courfe, but yet was in continual motion 

 to and fro, and all within a fpace not larger than the thicknefs of an 

 hair; whence I concluded, that, in the fmalleft branches, where 

 this velfel arofe, and in which the circulation w^as completed, the 

 blood was ftagnated, and thence its regular courfe in this veffel 

 impeded. 



The pleafure I derived from this fpedlacle was fo much in my 

 mind, that I was induced to a farther examination of the fubjecl, and 



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