422 PHILOSOPHICAL TRANSACTIONS. [aNNO l? iQ. 



whole bulk, and consequently that the blood globules make about ^ of the 

 whole. From which we shall find the specific gravity of the blood globules, to 

 be to that of water, as 1126 to 1000. 



If we suppose the blood globules to make ^, J-, ^, or -^ of the whole bulk, 

 their specific gravity will be respectively 1174, ] 150, 1102, or 1078. So that 

 on any of these suppositions, the specific gravity of the blood globules will be 

 considerably greater than that of the serum, and consequently they cannot be 

 supposed to be vesicles filled with an aerial substance. 



It will therefore perhaps be asked, what do they really consist of? In order 

 to come to a solution of this question, it may be proper to take notice, that 

 blood is composed of phlegm, oil, volatile and fixed salts, and earth.* For as 

 to the spirit, we consider it with Mr. Boyle, to consist of the phlegm and 

 volatile salt united together. That the serum, on a chemical analysis, exhibits 

 a great deal of the first of these, and the others in a very small quantity. That, 

 on the contrary, the crassamentum yields much less phlegm, but the other 

 principles much more copiously than the serum. 



From which data we may safely conclude, that the crassamentum, or globular 

 part of the blood, consists of some phlegm united with the oil and salts, and a 

 small quantity of earth. 



But what is the exact proportion of these several principles to each other ; 

 what alterations are produced in the body by a change of this proportion ; how, 

 and in what part these globules are formed ; by what means they preserve their 

 figure, without dissolving in the serum, or uniting with each other; what varia- 

 tions are made in their specific gravities by heat and cold ; and what are the 

 eflfects of those variations ; are questions not very easy to be solved, and yet of 

 so much importance to the animal economy, that it were greatly to be wished, 

 we had a number of data sufficient to determine them. 



P. S. Since this paper was sent to the press, I made the following experi- 

 ments, which serving to confirm the method last used, for finding the specific 

 gravity of the blood globules, it may not be improper to relate them. 



In August, I took a lump of the crassamentum, and washed it gently in fair 

 water, to free it from the loose globules, which precipitating out of the serum 

 after the coagulum is formed^ do not unite into one body with it. I then laid 

 it on a spongy brown paper, to drain off the superfluous moisture. After 

 which, weighing it first in air, and then in water, I found its specific gravity to 

 be 10834-. Another lump of the same crassamentum being weighed in the 

 same manner, its specific gravity was 1082,9. 



In September I found the specific gravity of another piece of crassamentum 



* See note respecting the component parts of the blood at p. 685, vol. ii. of this Abridgment. 



