12 BLOOD. 



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 puritication 

 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 eapillaries 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 

 eacn of which there are two or more kinds. The plasma holds in a dis- 

 solved state all the necessary materials for the nutrition, development, and 

 repair of the various tissues of the body. The red corpuscles impart to the 

 blood its characteristic colour, and their colouring matter (hoemoglohin) 

 carries oxygen from the air-cells of the lungs to the tissues throughout the 

 body. They constitute nearly one-half of the entire mass of the blood, and 

 are, in man, ffom 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. 



OOAGULATION O'F BLOOD.— If blood be withdrawn from the body, it 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 of Abrin, 

 and blood corpuscles which get caught and enclosed in the delicate network 

 formed by the fibrin. If the withaiawn blood, instead of being allowed to 

 spontaneously coagulate, be briskly stirred up with n, bundle ol twigs, the 

 hDrin, in place ol enclosing the blood corpuscles and becoming tnereby 

 more or less discoloured, will adhere to the twigs 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 pf 

 fibrin-ferment (which is contained in the white corpuscles) on a substance 

 (fibrinogen) 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 ol 

 tendons, ligaments, muscles, and the connective tissue underneath the skin, 

 resembles fibrin in composition. 



The serum of the blood has the property of rendering disease germs 

 inert, and thus protects the system Irom the invasion of these micro'bes. 

 Ewing ("The Lanoet," 19th May, 1894) remarks that "the loss of tihis 

 normal germicidal power helps us to explain the varying ra,pidity with 

 which post-mortem decomposition sets in. It is well known that the bodies 

 of persons who have died from different diseases , decompose with varying 

 degrees of rapidity. We cannot explain this differing rapidity of decom- 

 position simply by variations of temperature ; for under the same external 

 conditions, one body will be decomposed in a few hours, and another may 

 remain undeoomposed for several days." 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 virulent, as well as alive. Metchnikofi obtained a 

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

 an anthrax germ. The cultivation obtained was virulent. 



