64 PROPERTIES OF 



studious gentlemen, at that time living at the Middlesex Hos- 

 pital, and the appearances were exactly similar : and it was 

 evident to them that the blood in the saucers was later in co- 

 agulating than that in the cups, and that on the plates (one of 

 which was of pewter) was considerably later in jellying than 

 that in the cups or in the saucers. 



These experiments therefore show clearly, that the differences 

 in the periods of coagulation, and in the appearance of size 

 upon the blood received into the different cups in bleeding, 

 cannot be accounted for from a difference in the exposition to 

 air ', for here blood more exposed to the air than that is which 

 trickles down the arm is found equally sizy, and to be even 

 later in coagulating than blood less exposed. 



As we have here observed a new circumstance that appears 

 remarkable, and which at first sight seems not reconcilable to 

 some of our conclusions, it may therefore be necessary to examine 

 it farther, or to inquire, if air be a coagulant of the blood (as 

 we have endeavoured to prove in the beginning of this Essay) 

 how comes it that in this experiment the blood was not coagu- 

 lated proportionably to its exposition to the air ? This, I think, 

 may be explained from considering another fact that was men- 

 tioned in the preceding pages, viz. that cold lessens the blood's 

 tendency to coagulation. The blood, therefore, in the saucer, 

 although it was more exposed to the air, yet being more cooled 

 than that in the cup, was for that reason later in coagulating ; 

 and that on the plate, which was most exposed to the air, being 

 most cooled, was therefore latest of all. 



But we may add, that although it be evident from this ex- 

 periment, that the difference in the exposition to air, or to cold, 

 is not sufficient to explain the changes which we see produced 

 upon the blood, in so little time as in the filling of a small 

 cup, especially when those changes are so great as what are 

 mentioned in Experiment xxvn (where the blood in one cup 

 was thirty-five minutes in coagulating, and had a very thick 

 size, whilst that taken away soon after, coagulated in three mi- 

 nutes, and was without a size) yet, I think, that the effects of 

 air and of cold are considerable enough to deserve to be taken 

 into the account in some cases, where the changes on the blood 

 are not so great. For as cold thickens the blood, it is probable 

 that in some cases where the lymph is but little attenuated, 



