246 PHILOSOPHICAL TRANSACTIONS. [aNNO 1765. 



State. A small drop of blood was included between two talks, and was changed 

 during the observation, in order to give the appearance all the advantage that 

 might arise from the accidental situation of the globules between the talks, and 

 also to renew their motion ; for though the blood viewed in this manner is not 

 in a state of circulation, yet, either from the vacuum formed between the talks, 

 the attraction of their surfaces, or some other cause, the serum is seldom in a 

 quiet state on its being first included between them, and the globules that float 

 in it move for some time in various directions as the current of the serum 

 inclines them, or as they themselves are more or less attracted by each other or 

 by the talks, till the whole has found a state of rest. The magnifier applied 

 was a spherical glass, which he computed to magnify the object 512 times in 

 diameter. In these views, the globules, though they varied a little from each 

 other in their outlines and dimensions, appeared in general to be circular or 

 elliptic, and of the size of swan-shot. Their figure as solids was not easily to 

 be determined in such an exposition of them, but they had the appearance of 

 oblate spheroids much compressed, though, from their free motion with the 

 serum, it was manifest they suffered no pressure from the talks; where the 

 focus was perfect, or nearly so, the middle part of each globule was darker than 

 the margin ; and this difference in shade gave them an appearance, as if a dent 

 or concave impression had been made on their surfaces, which resembled those 

 of young peas that have dimpled in the boiling. What this darkness next the 

 centre was owing to, will appear from the 2d observation ; but in this I could 

 not judge it to arise from any thing but a sinking in of the surface in that part, 

 or some accident of the light that furnished such an appearance. 



July Qth, a 2d observation was made with the same instrument, to whicli 

 was applied a sphere which magnified the object 1 280 times in diameter. In 

 this view, the variation of shade on the middle part of each globule from that 

 of the margin, was such as carried with it strongly the appearance of a perfora- 

 tion. I had indeed my doubts of this on first examining them, because, on a 

 very slight alteration of the delicate focus of so high a magnifier, the light and 

 dark parts would interchange, so that the refraction or reflection of the light 

 might still be suspected to occasion the appearance in question: but continuing 

 my view stedfastly, and taking notice of all the diversities which a numerous 

 collection of globules presented, I remained at last thoroughly convinced that 

 they were perforated ; for, when any of the globules happened to move with the 

 serum in the most perfect focus, which could not happen to all, in a medium of 

 some little depth, I could with great clearness distinguish the exterior and in- 

 terior circumference of the ring, of which each globule consisted; the interior 

 one being bounded by a black line or shade next the perforation, exactly resem- 

 bling that which bounded the exterior one, and distinguished it from the serum 



