THE BLOOD. 59 



the last case we may likewise conclude, that although the times, 

 at which the blood taken from persons in health begins to 

 coagulate, be allowed to be about three minutes and a half, as 

 I have found from repeated observations, yet there may be some 

 variety in this respect ; for a plethora and other circumstances 

 may make it later in coagulating in some cases, even where the 

 patient is otherwise in perfect health. 1 



We have observed before that the size is sometimes very firm, 

 and at other times spongy and cellular ; these differences in its 

 density are, I suspect, in proportion to the degree of attenuation 

 and lessened disposition of the blood to coagulate ; for as the co- 

 agulation begins on the surface, and forms there a film which 

 attracts the rest of the lymph (see Note XLIV), the more that 

 lymph is attenuated, and the slower it coagulates, the more will 

 the film be able to separate it from the red globules, and from the 

 serum : thence perhaps it is, that when the blood, besides being 

 very thin, likewise jellies slowly (see Note xxi), we sometimes see 

 almost the whole coagulable lymph collected at the top, forming 

 a firm crust, which being free from the serum, as well as from 

 the globules, contracts the surface into a hollow form. But when 

 the blood has its disposition to coagulate less diminished in pro- 

 portion to the attenuation, then, although the globules subside 

 from the surface, yet the whole of the lymph jellies so soon 

 after the coagulation begins, that there is not time for its being 

 separated from the serum, of which it therefore contains a con- 

 siderable quantity, and is of course more spongy and cellular. 



In proportion to the thickness and density of the size, the 

 bottom of the cake is of a looser texture ; but this looseness of 

 texture is not owing to putrefaction, as has been suspected, but 

 merely to the lymph's being collected at the top, and therefore 

 leaving the bottom of the crassamentum. 



Notwithstanding bleeding does in general weaken the action 

 of the vessels, increase the disposition of the blood to coagulate, 

 and even thicken the lymph, yet it may happen that in the 

 ordinary quantity in which blood is taken away, none of these 

 effects shall be produced ; of this the following case seems to 

 be an instance. 



EXPERIMENT XXX. 



A woman in the seventh month of her pregnancy was bled 

 1 This inference is confirmed by a case mentioned below, Experiment xxxu. 



