il6 PHILOSOPHICAL TRANSACTIONS. [aNNO 17 IQ. 



and which stick to its surface, the crassamentum is kept from sinking, and 

 seems to float on the top of the serum. 



These accidents seem to have given the first occasion to that opinion, uhich 

 I think has been generally entertained by those who have written on this 

 subject, namely, that the globular part of the blood is specifically lighter than 

 the serum, in which it swims. 



But what has so fully established this persuasion, is the authority of the late 

 excellent Mr. Boyle, who, among the many valuable and curious experiments 

 he has given in his natural history of human blood, has left the following ones 

 on this subject; viz. the specific gravity of serum of human blood was found 

 by weighing a piece of sealing wax first in serum, and afterwards in water, to 

 be to the specific gravity of water, as 1024 to 1000. In a second experinient, 

 which for greater accuracy was made with an instrument contrived on purpose, 

 the specific gravity of serum was found to be to- that of water, as 11 94 to 

 1000. In a third experiment, made by the same instrument, and with serum 

 from the blood of another person, its specific gravity appeared to be 1186. 

 The medium between these last two experiments is 1 190, which has since been 

 universally received for the specific gravity of serum of human blood, the first 

 experiment being declared by Mr. Boyle himself to be less exactly made than 

 the others. The specific gravity of human blood was found by Mr. Boyle, to 

 be to that of water, as 1040 to 1 000; though on account of difficulties, by 

 him mentioned, he was far from being satisfied with this experiment, and re- 

 commended the thing to further trials. 



However, these experiments having hitherto past uncontroverted, and it 

 appearing from them, that the specific gravity of serum was greater than that 

 of blood, in the proportion of 1 190 to 1040, or of 8 to 7 nearly; it followed, 

 that the blood globules were specifically lighter than the serum, and that in a 

 very great degree, considering the small proportion that the bulk of the crassa- 

 mentum was found to bear to that of the serum, from other experiments. 



Hence it was conjectured, that these globules were thin vesicles filled with 

 an aerial substance: and this opinion seemed to receive a great confirmation, 

 on its being observed, in viewing the circulation by a microscope, that a 

 blood globule, in passing through a very narrow vessel, would change its shape 

 from a globular to an oval form, and would recover its former figure, as soon 

 as it was got through the narrow passage ; which appearance seemed to be na- 

 turally accounted for from the elasticity of the included aura. 



Upon this conjecture have been built a great many solutions of the phaeno- 

 mena observable in the animal economy, and its disorders ; the authors of 

 which have been led into this mistake by the natural consequence of a matter 



