140 Circulation of the Blood 



it is in some measure strained, and the thinner and 

 lighter part, which usually swims on the top and is the 

 most penetrating, is emitted. Thus, in phlebotomy, 

 when the blood escapes forcibly and to a distance, in 

 a full stream, and from a large orifice, it is thicker, has 

 more body, and a darker body ; but, if it flows from a 

 small orifice, and only drop by drop, as it usually does 

 when the bleeding fillet is untied, it is of a brighter 

 hue ; for then it is strained as it were, and the thinner 

 and more penetrating portion only escapes ; in the same 

 way, in the bleeding from the nose, in that which takes 

 place from a leech-bite, or from scarifications, or in any 

 other way by diapedesis or transudation, the blood is 

 always seen to have a brighter cast, because the thick- 

 ness and firmness of the coats of the arteries render 

 the outlet or outlets smaller, and less disposed to yield 

 a ready passage to the outpouring blood ; it happens 

 also that when fat persons are let blood, the orifice of 

 the vein is apt to be compressed by the subcutaneous 

 fat, by which the blood is made to appear thinner, more 

 florid, and in some sort arterious. On the other hand, 

 the blood that flows into a basin from a large artery 

 freely divided, will look venous. The blood in the 

 lungs is of a much more florid colour than it is in 

 the arteries, and we know how it is strained through 

 the pulmonary tissue. 



2d. The emptiness of the arteries in the dead body, 

 which probably misled Erasistratus in supposing that 

 they only contained aereal spirits, is caused by this, 

 that when respiration ceases the lungs collapse, and 

 then the passages through them are closed ; the heart, 

 however, continues for a time to contract upon the 

 blood, whence we find the left auricle more contracted, 

 and the corresponding ventricle, as well as the arteries 

 at large, appearing empty, simply because there is no 

 supply of blood flowing round to fill them. In cases, 

 however, in which the heart has ceased to pulsate and 

 the lungs to afford a passage to the blood simul- 



