414 



BLOOD. 



length, the clot extends as usual through the 

 whole mass, but it is colourless on its upper 

 part, and only red in the part into which the 

 globules have subsided. Professor Miiller 

 believes that the fibrine exists in a state of 

 solution in the serum, an opinion which to us 

 appears hardly reconcilable with the known che- 

 mical properties of this substance ; we are more 

 inclined to suppose that, like the proper glo- 

 bules, it is merely suspended in the mass of 

 the blood in a state of extreme subdivision, 

 and possessed of transparency too perfect to 

 admit of its being distinguished amidst the sur- 

 rounding fluid. 



There are circumstances under which the 

 blood only coagulates with difficulty, or in 

 which it even loses this property entirely. In 

 cases of poisoning with hydrocyanic acid, for 

 instance, the blood remains fluid and thick 

 after death ; the same thing also occurs after 

 death from fever of a typhoid type, from 

 lightning, &c. 



Another phenomenon presented by the 

 blood which is of very common occurrence, 

 and depends on the manner in which it coagu- 

 lates, consists in the formation of what is 

 called an inflammatory crust or buffy coat : 

 the coagulum, instead of being uniformly red, 

 then appears covered with a greyish or yel- 

 lowish viscid and very tough pellicle of 

 various degrees of thickness. The pheno- 

 menon in question is principally observed in 

 individuals labouring under acute inflammatory 

 affections of the serous or synovial membranes, 

 of the substance of the lungs, &c. but also 

 occurs among persons in good health, although 

 plethoric. The experiments of M. Ratier go 

 to prove that various circumstances, altogether 

 independent of the physiological state of the 

 individual, may also exert great influence on 

 the formation of the buffy coat : thus, cteteris 

 paribus, it is more readily produced if the 

 blood withdrawn be received in a deep and 

 narrow vessel, and if the opening in the vein 

 be large, and the jet be free. The cause of 

 the buffy coat has been very satisfactorily ex- 

 plained; it depends on the more rapid subsi- 

 dence than usual of the red globules, in con- 

 sequence of which the more superficial parts 

 of the coagulum contain none. From the ex- 

 periments of Professor Miiller it would also 

 appear that this subsidence of the globules 

 takes place more quickly if a thick solution of 

 gum be added to the blood, so as to increase 

 its density, whilst, when it is deprived of its 

 fibrine by stirring with rods, these bodies 

 remain for a very long time suspended . Now 

 it follows, from the investigations of Sir C. 

 Scudamore, that buffy blood contains a larger 

 proportion of fibrine than usual, a state to 

 which the more rapid deposition of the glo- 

 bules, and the formation of the inflammatory 

 crust, which is its consequence, may be at- 

 tributed. 



Thus far we have only spoken of the blood 

 in a general manner, and without respect to 

 the part of the system in which this fluid is 

 examined ; it is, however, very far from being 

 identical in every part, and there are wide 



differences between the physical and physio- 

 logical properties of arterial and of venous 

 blood. 



The blood which is tending to the several 

 parts of the body is in the first place of a 

 bright vermilion red colour (arterial blood); 

 whilst that which has already passed through 

 the different tissues, and is on its way back 

 from them, is of a dusky or blackish red of 

 various degrees of intensity (venous blood). 

 Arterial blood also coagulates more quickly 

 than venous blood, and, from the researches 

 of Dr. John Davy, appears to have rather a 

 less capacity for caloric,* and a somewhat in- 

 ferior specific gravity (1,049 : 1,051); we are, 

 however, led to think that in the normal state 

 the contrary of the latter proposition will be 

 found to obtain, for Messrs. Prevost and Du- 

 mas have shown that in this case arterial blood 

 contains a larger proportion of globules than 

 venous blood.f 



VVhen the physiological action of arterial 

 and of venous blood is investigated, still more 

 striking differences are discovered ; the first 

 maintains vital excitation in the economy, and 

 the second is insufficient to support life. 

 Physiologists have even gone so far as to 

 regard the influence of the venous blood upon 

 the brain as deleterious ; J but more recent 

 experiments show that though inadequate to 

 keep up life, it is far from being a poison ; 

 on the contrary, it rather tends to prolong 

 existence, for frogs whose vascular system is 

 filled with this liquid die less speedily than 

 those placed under similar circumstances, but 

 which have lost almost the whole of their blood 

 by haemorrhage. 



The blood thus modified by the influence 

 of the organs it permeates, is still susceptible 

 of resuming its primary colour, and of ac- 

 quiring at the same time its vivifying pro- 

 perties : it is enough to expose it to the con- 

 tact of oxygen, to give it back all its peculiar 

 qualities. We find, in fact, that if venous 

 blood be agitated with atmospheric air, 

 or better still with oxygen gas, it speedily 

 assumes the vermilion tint that characterizes 

 arterial blood, and if the air thus employed 

 be afterwards analysed, a certain quantity of 

 oxygen will be found to have disappeared, and 

 its place to be occupied with a corresponding 

 measure of carbonic acid. Now that which 

 happens here under the influence of mere 

 chemical affinity, also takes place in the ani- 

 mal economy, and it is even thus that venous 

 blood in being exposed to the contact of 

 atmospheric air in the respiratory apparatus, 

 whatever its nature, changes into arterial blood 

 and again becomes fit to minister to life. (See 

 RESPIRATION.) On the other hand, if ver- 

 milion-coloured blood be subjected to the 

 action of carbonic acid, it speedily acquires a 



* Philos. Trans. 1815. 



t Ann. de Chimie, t. xxiii. p. 67. 



| Bichat, sur la Vie et la Mort. See also the 

 article ASPHYXIA. 



M . Edwards, Influence des Agens Physiques 

 sur la Vie, translated by Dr. Hodgkin. 



