VOL. XXX.] PHILOSOPHICAL TRANSACTIONS. 41^ 



seasons of the year in which they were made. So that from them we may 

 safely determine the specific gravity of serum of human blood at a medium to 

 be 1029,5, or in a round number 1030; from which the greatest variation in 

 any of these experiments is little more than one in 1000; whereas the differ- 

 ence between Mr. Boyle's experiments and mine amounts to l6o in 1000. 



Exper. 12. — In April, in order to find the specific gravity of human blood, 

 which, by reason of its tenacity, and sudden alterations on standing, cannot be 

 determined by the hydrostatical balance ; I took a narrow-necked phial, and 

 filled it to a mark, with blood poured immediately out of the porringer, as soon 

 as the person was blooded This being weighed, as I had done the serum be- 

 fore, its specific gravity was found to be 1051. 



Exper. 13. — In August, having filled the same phial with the blood of an- 

 other person, running immediately out of the vein through a funnel, its specific 

 gravity was found to be 1053. Suffering this to stand till it was cold, I found 

 the blood was sunk a small matter below the mark in the neck of the phial. 

 This being filled up with the water, which in so small a quantity could make no 

 sensible difference from blood, I found the specific gravity of cold blood to 

 be 1055. 



Exper. 14. — In August, the last experiment being repeated in the same 

 manner, the specific gravity of cold blood was again found to be 1055. 



Exper. 15. — In July, the arterial blood, from which the serum was after- 

 wards drawn off for the llth experiment, being weighed in the same manner, 

 its specific gravity was 1052,5. 



As this arterial blood and its serum, differ no more in specific gravity from 

 venal blood and serum, than the several portions of these do from each other, 

 it is plain, that the difference in this respect between arterial and venal blood, is 

 wholly inconsiderable. 



In the 13th experiment it was observed, that the blood altered its specific 

 gravity on cooling from 1053 to 1055 ; from which we may infer, that if the 

 blood used in the 12th experiment had been suffered to stand till it was cold, its 

 specific gravity would have been 1053 : therefore, taking a medium among the 

 four last experiments, we may allow the specific gravity of cold human blood to 

 be 1054. 



The difference of 14 parts in 1000, between this and the specific gravity 

 determined by Mr. Boyle, is easily accounted for, if we consider, that that 

 gentleman did not make use of a vessel with a narrow neck, as plainly appears 

 from the circumstances mentioned in his experiment; and consequently a small 

 error in the height of the liquor would make a considerable alteration in the 

 specific gravity. 



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