80 INTRODUCTION. 



to the exit of the blood, and that it depended on its separation 

 from the colouring matter. The particles, are, in fact, com- 

 posed of central globules, transparent, whitish, and with a red 

 envelope, less diaphanous, formed like compressed spheres-, 

 The diameter of the particles, in the human species, is about 

 the one hundred fiftieth of a millimetre. As long as the blood 

 is contained in the vessels, and is in motion there, things re- 

 main in this state. 



74. The blood, out of its vessels, and while it retains its 

 warmth, exhales a vapour formed of water, and of an animal 

 matter susceptible of putrefaction. It soon coagulates, yield- 

 ing, probably, a little warmth, and gives out a large quan- 

 tity of carbonic acid gas. This disengagement of the gas, but 

 little sensible while the blood is subjected to atmospheric pres- 

 sure, manifesting itself only by the formation of canals in the in- 

 terior of the coagulum, takes place on the outside of the clot, 

 when it is placed under the exhausted receiver of the air 

 pump. We must not confound this extrication of gas and va- 

 pour from the blood when taken from its vessels, with a pre- 

 tended gas that has been supposed to circulate with it. 



Shortly after the blood has coagulated into a single mass, it 

 separates into two parts; the coagulum contracting, presses out 

 the fluid part or the serum, it contained. This contraction 

 continues, and consequently, the quantity of this expressed se- 

 rum augments until putrefaction takes place. Generally the 

 upper surface of the coagulum, contracting more than the rest, 

 becomes concave. If the clot be held for a long time under a 

 small stream of water and gently pressed, the water carries 

 away the colouring matter or cruor, and there remains a white 

 fibrous mass. Thus by coagulation and washing, the blood is 

 divided into serum, cruor, and fibrine. 



But let us see what takes place during these operations: as 

 soon as the blood is out of its vessels, the colouring matter of 

 the particles leaves the central white globules, and tho latter, 

 deprived of their envelope, unite to each other and form fila- 

 ments which interweave themselves, forming a net-work, in 

 which are contained both the colouring matter, and many en- 

 tire particles that have not undergone this decomposition. 



