LIX. Centrifugalizing the blood. To determine the rela- 

 tive volume of red corpuscles and plasma. 



1. Appliances. Daland's haematocrit (Fig. 43); small rub- 

 ber tubing to fit capillary tube; needle and holder; vase- 

 lin; white paper. 



2. Preparation. Adjust rubber to capillary tube. Put 

 empty tube in one arm of crosspiece to preserve bal- 

 ance. 



j. Operation. Obtain blood from the lobe of the ear as 

 heretofore described. Draw capillary tube full of blood. 

 Grease the finger with vaselin and hold over the free 

 end of the tube before drawing off the rubber. Place the 

 tube in the crosspiece of the instrument as quickly as 

 possible and revolve at least two minutes at the rate of 

 seventy turns per minute. Take out the tube and lay 

 on a piece of white paper to read the divisions. Each 

 degree of the scale is estimated to contain about 100,000 

 cells; hence, a tube in which the red column stands at 

 50 would indicate about 5,000,000 red corpuscles per 

 cubic millimeter. The use of this instrument is de- 

 signed chiefly to show the volume of red corpuscles rather 

 than the number^ as shown by the Thoma-Zeiss counter. 



4 Precautions. See that the instrument is securely at- 

 tached to the table and the crosspiece to the instru- 

 ment before setting it in motion. 



5. Observations and Problems. 



(1) Determine the volume per cent of red blood cor- 

 puscles in a number of normal individuals. 



(2) Do apparently normal individuals have the same or 



270 



