THE BLOOD-CORPUSCLES 23 



in corpuscles than that which leaves them. The lymphatic glands, 

 however, although the principal, are not the only seat of formation 

 of lymphocytes, for lymph contains some corpuscles before it has 

 passed through any gland ; and although a certain number of these 

 may have found their way by diapedesis from the blood, others are 

 developed in the diffuse adenoid tissue, or in special collections of it, 

 such as the thymus, the tonsils, the Peyer's patches and solitary 

 follicles of the intestine, and the splenic corpuscles. To a very 

 small extent white blood-corpuscles may multiply by karyokinesis 

 or indirect division in the blood. 



The fate of the leucocytes is even less known than that of the 

 red corpuscles, for they contain no characteristic substance, like 

 the blood-pigment, by which their destruction may be traced. That 

 they are constantly disappearing is certain, for they are constantly 

 being produced. Not a few of them actually escape from the 

 mucous membranes of the respiratory, digestive, and urinary 

 tracts. The remnants of broken-down leucocytes have been found 

 in the spleen and lymph glands. It must be assumed that many 

 break up in the blood-plasma itself. 



SECTION II. GENERAL PHYSICAL AND CHEMICAL PROPERTIES OF 



THE BLOOD. 



Fresh blood varies in colour, from scarlet in the arteries to 

 purple-red in the veins. It is a somewhat viscid liquid, with a 

 saline taste and a peculiar odour. 



Viscosity of Blood. The viscosity of normal dog's blood is about 

 six times greater than that of distilled water at body temperature. 

 It can be determined by allowing the blood to flow through a capil- 

 lary tube of known dimensions under a definite pressure, and 

 measuring the amount which escapes in a given time. In general 

 the viscosity and specific gravity of the blood vary in the same 

 direction, although there is not an exact proportionality between 

 them. Thus, sweating, which causes a diminution of the water of 

 the blood, causes also an increase in its viscosity. With increasing 

 temperature the viscosity of the blood diminishes, as is the case 

 with other liquids (Burton-Opitz). 



In polycythaemia, where the number of erythrocytes in propor- 

 tion to plasma is greatly increased, the viscosity of the blood in- 

 creases in an equal degree. In one case of polycythaemia, with a 

 blood-count of 8,300,000, the viscosity was 9-4 times that of water; 

 in a case of marked chlorosis it was only 2-14. But the importance 

 of this factor in causing an abnormal blood-pressure by increasing 

 or diminishing the resistance to the blood-flow has been exaggerated. 

 Although it has been shown that in the living vessels, so long as 



