BODY TISSUES AND FLUIDS 



COMPOSITION OF HUMAN BLOOD (Continued) 



425 



that these changes should be very marked except in severe pathological 

 conditions. With sufficiently delicate methods, however, these slight 

 changes should be readily detected. The development of simple and very 

 delicate colorimetric methods has done much to aid in this type of work. 



More and more we have come to consider the various changes which 

 take place in the body from a quantitative point of view. The various 

 blood constituents, and certain blood determinations, with the range of 

 their normal and pathological variations, are given in the table above. 



Blood Volume. Owing principally to the recent work of Keith, Rown- 

 tree and Geraghty the subject of blood volume has received considerable at- 

 tention. These investigators have introduced a new method of deterinin* 

 ing blood volume and have obtained somewhat higher figures than those 

 formerly given for man. The principle underlying their method is the 

 introduction directly into the circulation of a non-toxic, slowly absorbable 

 dye (vital red) which remains in the plasma long enough for thorough 

 mixing, and the determination of its concentration in the plasma colori- 

 metrically by comparison with a suitable standard mixture of dye and 

 serum. According to this method the plasma normally constitutes ap- 

 proximately 5 per cent, or one-twentieth of the body weight. The volume 

 occupied by the corpuscles was calculated with the aid of the hematocrite 

 and found to average 43 per cent for the erythrocytes and 57 per cent for 

 the plasma. On this basis Keith, Eowntree and Geraghty have calculated 

 that blood normally constitutes 8.8 per cent or 1/11.4 of the body weight. 

 With this method they were able to demonstrate the amount of decrease in 

 blood volume as the result of hemorrhage and of the increase following 

 intravenous infusion of saline. 



Significant observations were made in a few pathological conditions. 

 Both the blood and plasma volume are increased in pregnancy, before, 

 term, but return to normal within a week or two after delivery. In obesity 

 the plasma and blood volumes arc relatively small. Many cases of anemia 



