86 THE BLOOD AND THE LYMPH 



methods give the total amount of blood in the body as from 5 to 8.8 per 

 cent of its weight. Meek has recently developed a method in which gum 

 acacia is used. After mixing with the blood, the concentration of this 

 substance is determined from the calcium content. Being colloid, none 

 of the gum leaves the blood vessels. 



The vital red method is employed as follows: A 1.5 per cent solution of vital red is 

 preserved in sterile condition in 15-20 c.c. quantities. A needle is inserted in the 

 basilic vein and 6-8 c.c. of blood withdrawn into a dry syringe containing finely pow- 

 dered pot. oxalate. The syringe is removed from the needle, and another syringe con- 

 taining an amount of the vital red solution corresponding to 3 mg. vital red per kilo body 

 weight, is connected with the needle and the dye slowly injected. The blood removed 

 in the first syringe is now transferred to a paraffined centrifuge tube, and in about 

 10 minutes a third syringe is connected with the needle and 8-10 c.c. of blood removed 

 and transferred to two paraffined tubes. From one of these a specimen is taken for 

 the hematocrit. The tubes are then centrifuged rapidly for some time. The dilution 

 of dye in the plasma is now determined colorimetrically, using 1 as a stanclard the fol- 

 lowing: 1 c.c. diluted dye (0.5 e.c. of the original dye solution to 100 c.c. 0.8 per cent 

 NaCl sol.) 



1 c. c. plasma before injection 



2 c. c. 0.8 per cent NaCl. 

 and using as test .solution 



1 c. c. plasma after dye injection 



3 c. c. 0.8 per cent NaCl. 

 The formula for calculation is 



200 



- X c - c - dye injected X 10 = c - c - plasma 

 E 

 Where R per cent reading of test solution. 



By use of the above method Keith, Rowiitree and Geraghty found that 

 in man the plasma normally constitutes 5 per cent or % the body weight, 

 i.e., 50 c.c. plasma per kg. 



To determine total blood volume the hematocrit must also be used, and 

 it was found that the total volume = 8.8 per cent or l/11.4th of body 

 weight. Normal individuals therefore have 85 c.c. blood per kg. 



In pregnancy, before term the blood and plasma volumes are increased, 

 but within a week or so of delivery the volumes return to normal. In 

 obesity the plasma and blood volumes are relatively small. Many cases 

 of anemia exhibit a relatively larger plasma volume. Hypertension may 

 be accompanied by a small blood volume, therefore this condition is not 

 due to large blood volume. 



The newer methods have shown that the volume of the circulating 

 fluid is maintained fairly constant in spite of influences tending to alter 

 it. The body accomplishes this by drawing upon the reserve fluid in 

 the tissues and by varying the rate of water excretion, particularly 

 through the kidneys. Years ago the doctrine of an increased amount of 



