258 THE BLOOD AND THE LYMPH 



THE CHEMICAL COMPONENTS OF THE THROMBOCYTES, Or platelets, 



because of the smallness and fewness of these floating particles, is not 

 definitely known. They consist perhaps chiefly of nucleo-proteid, or of 

 globulin. Biirker has recently shown by quantitative and gravimetric 

 methods that, whatever their composition, the fibrin of coagulation 

 probably comes from them (see discussion of coagulation on page 260). 

 WHOLE BLOOD, or, more simply, blood, is a "tissue" of the body in 

 which the morphological " matrix" is a liquid with important functions, 

 the contained cells being the three sorts already noted. It constitutes 

 about 7 per cent, by weight of the human body. Its specific gravity 

 is from 1050 to 1062, that of women and children ranging from the lower 

 number to 1055, and man's from 1057 to 1062. The specific gravity of 

 the corpuscles is about 1105, and of the plasma not far from 1030. In 

 chemical reaction blood is always alkaline because of its plasma's sodium 

 phosphate and carbonate. The mean alkalinity of the blood is about 

 equal to that of 0.4 per cent, solution of sodium hydrate. It is lowest 

 in the morning and highest at night. Owing to the passage into the 

 circulation of lactic acid (from the decomposition of the muscle's proteid), 

 bodily exercise decreases the blood's alkalinity. In color blood varies 

 from the dull scarlet of the pulmonary vein, leading from the air in the 

 lungs, to the purplish red of the pulmonary artery, leading from the 

 oxygen-reducing tissues. The tinge then depends on the proportion of 

 oxygen in the erythrocytes. The color-difference in health is much less 

 than is generally supposed by those who use anatomical text- books with 

 colored plates. It is in mass only that blood is red. No redness is per- 

 ceptible in the capillaries, and the file of erythrocytes there is of a light 

 straw-yellow color; yet it is from masses of these corpuscles that the 

 redness of blood comes. In taste blood is saline, this being due largely 

 to the sodium chloride of the plasma. The odor of blood is character- 

 istic, and is largely caused by the various volatile fatty acids and the 

 traces of excretory products present. The viscidity of blood is due to its 

 composition and, soon after shedding, to commencing coagulation. 

 Blood is markedly opaque, as is inevitable in a colored liquid containing 

 so many opaque bodies in suspension. The temperature of the circulating 

 blood varies more than a degree in different bodily parts. It is highest 

 where the blood is coming from the actively metabolic liver, the largest 

 single heat-producer in the organism. The blood constitutes one-twelfth 

 or one-thirteenth of a man's body weight, a man of average size having 

 then about five liters of blood in his body. The loss of one of these 

 liters would ordinarily kill him, but a woman might lose proportionally 

 somewhat more and survive. The blood's distribution in general is 

 about as follows (Ranke) : One-fourth of it is in the circulation including 

 the lungs, another fourth in the skeletal muscles, another in the liver, 

 and the remaining quarter is apportioned among the other parts of the 

 body. During inanition the blood sometimes becomes more concen- 

 trated, the proportion of erythrocytes somewhat greater, the number 



