Organs of Respiration and Circulation. 



577 



a greater quantity than domesticated, and those which are fat less 

 than those which are lean. The redness of these corpuscules is 

 due to the presence of a red pigment, hoimatosin, which is diffused 

 in the fluid which distends their walls, and it is in consequence of 

 this pigment being chemically acted upon in the minute vessels 

 of the system by the carbonic acid, and in those of the lungs by 

 the oxygen, that the difference in the colour of arterial and venous 

 blood is observed. The change in the colour of the blood is 

 likewise connected with the process which generates animal heat 

 — facts which we shall again advert to. 



We pass onwards to speak of the fibrine of the blood. It 

 is generally known that very shortly after the withdrawal of 

 blood it clots or coagulates into a tolerably firm mass ; this is 

 owing to its fibrine, and in no way depends on any other of its 

 constituents. This peculiar quality of the fibrine has led to its 

 being called self-coagulating lymph — a term very rarely employed 

 in the present day. It is only by abstracting blood that we are 

 enabled to obtain this material, and to investigate its properties. 

 Various means are had recourse to for this purpose, such as filter- 

 ing the blood while it is fluid, washing the crassamentum or clot, 

 or stirring the blood while it is undergoing coagulation. The 

 latter is the plan usually adopted ; and if a small bundle of twigs 

 are used for the purpose, it will be observed that the fibrine will 

 adhere to them more or less in a colourless condition, leaving 

 behind the serum and red particles.* Washing the mass thus 

 obtained renders it white by removing the colouring matter from 

 the few red particles which were entangled in its meshes while 

 coagulating. An examination of the fibrine shows not only that 

 it is white, but also that it is very tough and elastic, and, when 

 viewed by a magnifying lens, it is found to be made up of fibres 

 which intersect each other in every possible direction. The 

 fibril! ating or self- coagulating power of this material serves most 

 important purposes in the animal economy. It forms the tem- 

 porary bond of union between broken bones, and plugs to arrest 

 the flow of blood from vessels which have been lacerated or torn 

 asunder: and were it not for this, death would frequently result 

 from causes which are now nearly inoperative. Fibrine may 

 justly be described as the basis of the animal machine; and 

 as its appropriation takes place during its circulation through the 

 capillary blood-vessels, and as these form the connecting link 

 between the arteries and the veins, so it will be apparent that 

 venous blood must contain a smaller portion of it than the arterial. 

 The relative quantity in these vessels is calculated by Midler to 

 be in the proportion of 29 to 24. In health, about 3 parts of 



* Some fibrine thus obtained was exhibited at the lecture. 



