PART II 

 THE BLOOD AND THE LYMPH 



CHAPTER X 



BLOOD: ITS GENERAL PROPERTIES 

 BY R. G. PEARCE, B.A., M.D. 



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 most accurate method of determining the volume of blood in 

 the body is 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 deter- 

 mining the total volume of blood are based upon the principle of add- 

 ing a definite quantity of a knoAvn 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 estimating its concentration in a sample of blood withdrawn from the 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 and does not cause fluid to be withdrawn from the tissues, the total quantity 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 carbon monoxide gas 

 is inhaled in a given amount and the carbon monoxide hemoglobin sub- 

 sequently determined colorimetriealjy ; and Keith, Rowntree and Ger- 

 aghty's, 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 



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