12 BLOOD. 



Vierordt, the blood of the hor?e takes about 31 seconds of time, and about 27 

 contractions of the heart to complete the entire round. 



The circulation of blood from the left ventricle to the right auricle is called 

 the general circulation ; that from the right ventricle to the left auricle, the 

 pulmonary circulation. The former is concerned with the general nutrition 

 of the body, including the lungs ; the latter, with the purification of the 

 blood by means of the air-cells. The heart, arteries, capillaries and veins 

 thus form a system of pipes through which the blood circulates. The walls 

 of these vessels, with the exception of those of the capillaries and the very 

 small veins, are practically impervious to fluid. 



BLOOD. — Blood is formed of a watery fluid (plasma or liquor sanguinis) 

 and microscopic bodies (blood corpuscles) which float in it. The blood 

 corpuscles consist of red corpuscles and white corpuscles (leucocytes), of each 

 of which there are two or more kinds. The plasma holds in a dissolved state 

 all the necessary materials for the nutrition, development, and repair of the 

 various tissues of the body. Tlie red corpuscles impart to the blood its 

 characteristic colour, and their colouring matter (hcemoglobin) carries oxygen 

 from the air-cells of the lungs to the tissues throughout the bod}'-. They consti- 

 tute nearly one-half of the entire mass of the blood, and are, in man, from 500 

 to 600 times more numerous than the white corpuscles. The leucocytes have the 

 power of amoeboid movement, and of taking into their substance and digesting 

 other microscopic bodies ; thus acting as scavengers for the removal of waste 

 matters, and to some extent as protectors of the tissues against the attacks 

 of disease germs. They (or at least, one or more varieties of them) contain 

 fibrin-ferment, to which I shall allude in the following paragraph. 



COAGULATION OF BLOOD.— If blood be withdrawn from the body, it 

 will under ordinary circumstances, gradually separate into a solid mass (clot) 

 and an amber-coloured fluid (serum). The clot consists O'f ^hrin, and blood 

 corpuscles which get caught and enclosed in the delicate network formed by 

 the fibrin. If the withdrawn blood, instead of being allowed to vspontaneously 

 coagulate, be briskly stirred up with a bundle of twigs, the fibrin, in place 

 of enclosing the blood corpuscles and becoming thereby more or less dis- 

 discoloured, will adhere to the tAvigs in the form of elastic, fibrous threads, 

 which will become white on being washed in water. Fibrin does not exist as 

 such in the blood ; but is produced by the action of fibrin-ferment (which is 

 contained in the white corpuscles) on a substance (^brivogcn) which is held in 

 a dissolved state in the plasma (Hammersten). It seems that under usual 

 conditions, this ferment is not set free as long as the leucocytes remain in the 

 blood-vessels. The white fibrous tissue of tendons, ligaments, muscles, and 

 the connective tissue underneath the skin, resembles fibrin in composition. 



Buchner, Nuttall, von Fodor, and others maintain that the serum of the 

 blood has the property of rendering disease germs inert, and thus protects the 

 system from the invasion of these microbes. Ewing (" The Lancet," 19th 

 May, 1894) remarks that " the loss of this normal germicidal power helps us 

 to explain the varying rapidity with which post-mortem decomposition sets 

 in. It is well known that the bodies of persons who have died from diff'erent 

 diseases decompose with varying degrees of rapidity. We cannot explain this 

 differing rapidity of decomposition simply by variations of temperature ; for 

 under the same external conditions, one body will be decomposed in a few 

 hours, and another may remain undocomposed for several days." Cadeac 

 remarks that the microbes which are taken by the phagocytes (leucocytes and 

 the cells of the tissues) are alive. In fact, we may see, under the microscope, 

 these bacilli moving in their living prison. If the phagocyte be dead, we may 

 observe the microbe which it surrounds, elongating itself, and escaping. The 

 microbes seized by the phagocytes may be vimlent, as well as alive. Metchnikoff 

 obtained a cultivation of anthrax by sowing in broth a leucocyte which had 

 enveloped an anthrax germ. The cultivation obtained was virulent. 



