BLOOD. 



413 



Lastly, the composition of the blood may 

 also vary in the same individual according to 

 a variety of circumstances. Prolonged absti- 

 nence from diluents, for example, tends to di- 

 minish the proportion of the watery particles 

 of the blood, and, consequently, to render it 

 richer in nutrient elements. Bloodletting pro- 

 duces the contrary effect; not only is the mass 

 of circulating fluid by this means diminished, 

 but it is also rendered poorer. Messrs. Prevost 

 and Dumas having bled a cat largely, found 

 its blood to consist of 791 of water, 87 of 

 albumen, and 118 of globules. Two minutes 

 afterwards they repeated the bleeding, and now 

 only found 116 of globules, and 74 of albu- 

 men to 809 of water ; after an interval of five 

 minutes more the bleeding was repeated for 

 the third time, and they found the blood to 

 consist of 829 of water, 93 of solid particles, 

 and 77 of albumen. M. Lecanu obtained 

 similar results from the analysis of human 

 blood taken from patients who had been bled 

 several times in quick succession, or who were 

 labouring under haemorrhagic affections ;* and 

 the circumstance is readily explained, by sup- 

 posing that the diminution of the mass of 

 blood tends to accelerate absorption, the first 

 effect of which must needs be to introduce a 

 much larger proportion of water than of solid 

 particles into the torrent of the circulation. 



In its ordinary state the blood is always 

 fluid, and consists, as we have seen, of a 

 watery part, holding solid globules in suspen- 

 sion; but under certain circumstances its physical 

 properties change completely: this happens 

 whenever it is withdrawn from the vessels in 

 which it is contained in the bodies of living 

 animals, or in the event of an animal ceasing 

 to exist. The blood left to itself changes within 

 a few minutes into a mass of a gelatinous con- 

 sistence, which gradually separates into two 

 parts, one fluid, transparent, and of a yel- 

 lowish colour, formed by the serum ; another 

 solid, quite opaque, and of a red colour, to 

 which the name of cruor, crassamentum, or 

 clot is given. 



The mode in which this phenomenon hap- 

 pens, and the cause that occasions it, have 

 engaged the attention of a great many physio- 

 logists. The experiments of Hunter and of 

 many others show that the coagulation of the 

 blood depends mainly on the cessation of the 

 motion to which it is constantly subjected in 

 the course of the circulation ; for this condition 

 alone suffices to make it coagulate even in the 

 interior of the vascular system, and we are of 

 opinion that the great physiologist just quoted 

 erred in attributing vital properties to the blood. 

 Rest, then, cessation from motion, is that 

 which contributes most generally and most 

 essentially to cause coagulation of the blood ; 

 other circumstances, however, such as its 

 cooling, its being brought into contact with 

 the air, &c. may also contribute to accelerate 

 this phenomenon, which appears, from the 

 experiments of Dr. John Davy, to be unac- 

 companied with any evolution of caloric. 



If a clot of blood be gently kneaded and 

 pressed under a stream of water, it gradually 

 becomes paler, and finally loses its red colour 

 entirely, the colouring matter being washed 

 away; what remains in the hand is a mass of 

 whitish and very elastic filaments composed of 

 fibrine. Or otherwise, if, instead of being left 

 at rest, a quantity of freshly drawn blood be 

 quickly stirred with a bundle of rods, a stringy 

 mass of fibrine will be found adhering to these 

 after a time, and the blood thus treated will 

 not coagulate. This experiment shows that it 

 is to the fibrine that the blood owes its pro- 

 perty of coagulating. 



The filaments of fibrine studied under the 

 microscope are found to be formed by the 

 aggregation of a multitude of white globules, 

 bearing the greatest resemblance to the central 

 nuclei of the proper globules of the blood. 

 It was, therefore, natural to suppose that the 

 formation of the coagulum depended on the 

 spontaneous decomposition of these globules 

 and the aggregation of their internal corpuscles. 

 And such, indeed, is the theory which Messrs. 

 Prevost and Dumas have given, and which 

 has been adopted by the greater number of the 

 physiologists of the present day. " The at- 

 traction," say they, " which keeps the red 

 matter fixed around the white globules having 

 ceased along with the motion of the fluid, these 

 globules are left at liberty to obey the force 

 which tends to make them combine and form 

 a net-work, in the meshes or amid the plates 

 of which the colouring matter is included along 

 with a great quantity of particles which have 

 escaped this spontaneous decomposition."* 



It would appear, however, that this is not 

 an exact explanation of the phenomenon, for 

 Professor Miiller, of Berlin, has succeeded in 

 demonstrating that the coagulation of the blood 

 is altogether independent of the globules, and 

 that the fibrine which determines the pheno- 

 menon exists dissolved in the serum. By filter- 

 ing with great care the blood of frogs, diluted 

 with sugar-water, he separated the globules 

 completely from the serum before coagulation 

 took place : the fluid part of the blood alone 

 passed the filter, the solid particles remained 

 upon it; nevertheless, a coagulum formed 

 within the fluid after the lapse of a few mi- 

 nutes; this, of course, was colourless instead 

 of red, as it is when the red globules are en- 

 tangled in the mass. This curious and in- 

 teresting experiment does not succeed so well 

 when human blood is employed, inasmuch 

 as the globules, being much smaller than those 

 of the blood of the frog, pass along with the 

 serum through almost any filter that can be 

 used. Still Professor Miiller has succeeded 

 in proving the existence of fibrine in the serum 

 by means of the following procedure. If to a 

 little blood contained in a watch-glass a few 

 drops of a highly concentrated solution of sub- 

 carbonate of potash be added, the coagulation 

 of the fluid is so much retarded, that the glo- 

 bules have time to sink to the bottom before it 

 occurs. When coagulation takes place at 



* Journal de Pharraacie, 1831. 



* Ann. de Chimie, t. 23, p. 51. 



