THE RED CORPUSCLES. 103 



any volume can be found by multiplication. Several different 

 solutions have been proposed for the dilution of the blood, one of 

 the most convenient being a 3-per-cent. solution of sodium chlorid. 

 For clinical purposes the blood is best obtained from the tip of the 

 finger on the lobe of the ear. For testing the method defibrinated 

 blood from the slaughter-house may be employed. The dilution 

 may be made twice as great by filling the capillary only to the 0.5 

 mark and diluting as before. In this case the number of corpuscles 

 in each square must be multiplied by 8000 to give the number in a 

 cubic millimeter. 



The average number of red corpuscles normally present is 

 5,000,000 per cubic millimeter in the case of a man, and 4,500,000 per 

 cubic millimeter of a woman. This may vary greatly in disease. 



222. DETERMINATION OF THE NUMBER OF RED BLOOD- 

 CORPUSGLES. Fill the capillary tube of the pipette with blood 

 to the mark 1, drawing it in slowly by suction with the mouth 

 and avoiding the presence of air-bubbles in the tube. Quickly 

 wipe dry the end of the pipette with filter-paper and draw in 

 the diluting salt-solution (3 per cent.) to the mark 101. Close 

 the lower end of the pipette witl* the finger, then compress the 

 rubber tube at the upper end of the pipette and shake to thoroughly 

 mix the fluids. The small glass bead in the bulb aids in this mix- 

 ing. Allow the salt solution to flow out of the capillary, place a 

 drop of the diluted blood on the ruled side and cover it with a 

 cover-glass so that air-bubbles are not inclosed. When the cor- 

 puscles have come to rest, count the number in all sixteen squares. 

 Count those upon the upper and left hand line of each square as 

 belonging to the square. Use an objective which will magnify 

 100 to 200 diameters. The squares should be taken in some definite 

 order to avoid counting the corpuscles in the same one more than 

 once. The average number of corpuscles multiplied by 4000 gives 

 the number in a cubic millimeter of the diluted blood. Multiply 

 this by 100 for the original blood. Since a slight error in the 

 average of each square would make a considerable error when 

 multiplied by 4000, it is advisable to repeat the filling of the cell 

 several times before taking the average. After using, the pipette 

 should be rinsed out first with the diluting salt solution, then suc- 

 cessively with water, alcohol, and ether, and finally dried by blow- 

 ing dry air through it. 



