PART II 

 THE BLOOD AND THE LYMPH 



CHAPTER X 



BLOOD: ITS GENERAL PROPERTIES 

 (Partly Contributed by R. G. PEARCE) 



The blood, being the carrier of the nutritive and waste substances of 

 the body's metabolism, must at one time or another contain all the ma- 

 terials which compose the tissues in addition to those which are peculiar 

 to the blood itself. It is a very complex fluid, and all of its constituents 

 are not fully known. Structurally it is composed of water in which are 

 dissolved various gases and organic and inorganic bodies, the corpuscles 

 and platelets. 



THE QUANTITY OF BLOOD IN THE BODY 



The volume of blood in the body may be measured by bleeding and 

 subsequently washing out the blood from the vessels and then estimating 

 the amount of hemoglobin in the total fluid (Welcher's method). This 

 method employed in the case of two criminals who had been decapitated 

 gave the weight of the blood as 7.7 and 7.2 per cent of the body weight. 

 Bloodless methods for determining the total volume of blood are based 

 upon the principle of adding a definite quantity of a known substance to 

 the circulation and then estimating its concentration in a sample of blood 

 withdrawn from the body shortly afterward. If the substance can not 

 leave the blood vessels and does not cause fluid to be withdrawn from the 

 tissues, the total quantity of blood in the body can be calculated from the 

 concentration of the injected substance in the blood. The most accurate 

 methods based on this principle are Haldane and Smith's, in which car- 

 bon monoxide gas is inhaled in a given amount and the carbon monoxide 

 hemoglobin subsequently determined colorimetrically ; and Keith, 18 Rown- 

 tree and Geraghty's, 20 which employs vital red, a dye of low diffusibility. 

 The dye remains long enough in the body to be thoroughly mixed with the 

 blood, and its concentration in the plasma is determined colorimetrically 

 by comparing with a suitable standard mixture of dye and serum. These 



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