22 PROPERTIES OF 



it probably is in this way that the blood is coagulated in the 

 body, I have been more particularly attentive to it, and have 

 endeavoured to determine by experiment how it takes place. 

 With this view I have several times repeated Experiment the 

 Fourth, which was made with a view to determine whether the 

 blood would coagulate by -rest. In the first trial, the vein 

 was not opened till the end of three hours and a quarter ; and 

 just before it was opened I had observed through its coats, that 

 the upper part of the blood was transparent, owing to the separa- 

 tion of the lymph. On letting out this blood, it seemed to me 

 entirely fluid : a part indeed had been lost, but the greatest part 

 was collected in the cup, and which afterwards coagulated as 

 blood commonly does when exposed to the air. From this 

 experiment I imagined that the whole had been fluid ; but 

 from others made since, I am persuaded that the part which 

 was lost had been coagulated ; for, from a variety of trials, I 

 now find, that though the whole of the blood is not congealed 

 in this time by rest alone, yet a part of it is. But as it would 

 be trespassing too much on the reader's time to relate every 

 experiment I have been obliged to make for this purpose, I 

 shall only mention the general result of the whole. 



After fixing a dog down to a table, and tying up his jugular 

 veins, I have in general found that on opening them at the 

 end of ten minutes, the blood was still entirely fluid, or with- 

 out any appearance of coagulation. 1 If they were opened at 

 the end of fifteen minutes, at first sight it also appeared quite 

 fluid; but on a careful examination I found sometimes one, 

 and sometimes two or three small particles about the size of a 

 pin's head, which were coagulated parts of the blood. When 

 opened later than this period, a larger and larger coagulum 

 was observed; but so very slowly does this coagulation pro- 

 ceed, that in an experiment where I had the curiosity to com- 

 pare more exactly the clotted part with the unclotted, I found, 

 after the vein had been tied two hours and a quarter, that the 

 coagulum weighed only two grains ; whilst the rest of the 

 blood, which was fluid, on being suffered to congeal, weighed 



1 I say in general it was fluid at the end of ten minutes ; but I must likewise 

 mention that in one dog I found two very small particles of beginning coagulation, 

 even at this period ; yet in another I could not observe any such appearance, even at 

 the end of fifteen minutes. 



