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I alfb examined larger Frogs, and in their feet I law the circula- 

 tion of the blood, but with much difficulty, and, unlefs I had be- 

 fore difcovered it in the fmall ones, it would have been impoffible 

 for me to difcover the complete circulation in the fmallest vellels. 

 But when I examined other parts of the bodies of thefe larger Frogs, 

 I there completely dilcovered the circulation. 



Among other things, I at one time faw the blood in an artery 

 (large enough to admit three globules of blood at a time) driven in 

 a contrary direction to the ordinary one; but this retrograde motion 

 lafted no longer than while one could tell four, after which it re- 

 fumcd its ufual courfe. To illullrate this : I faw the blood running 

 as defcribed in fig. 25, N R O P, palling from N to O ; out of which 

 artery arofe a branch or fmall artery ; but here the light which at- 

 tracted my notice was, that the blood in the artery, P Q, not only 

 fuddenly flopped in its motion, but was driven back from Q to P, and 

 emptied into the artery N R O P. The caufe of this, I think, might 

 be, that the blood in the fmall artery, P Q, or in the fmaller branches 

 into which the artery, P Q, was divided, had met with fome fmall 

 obftruftion, or that fome mufcle, adjoining to thefe fmall vellels, 

 fo prelled upon them, that the courfe of the blood was thereby im- 

 peded, whence the blood was not only llopped in its progress, but 

 driven by a backward motion into the artery adjoining ; for, after 

 the lliort time I have mentioned, the blood relumed its motion in 

 the fame courfe and with the fame fwiftnefs as before. 



In another place I faw the courfe of the blood, in the fame kind 

 of artery, very much retarded for a fliort fpace, and immediately 

 afterwards in the fame artery a fudden protrulion, and diredlly after- 

 wards another Hop or lliort interruption in the circulation. This pro- 

 trufion and interruption took place live or fix times fuccelTively, af- 

 ter which followed a fwift and regular motion, and all this was per- 

 formed in fo lliort a fpace of time, that I could fcarcely have fpoken 

 ten words in the interval. 



