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PHYSIOLOGICAL CHEMISTRY 



square as belonging to that square. Take the squares in some definite se- 

 quence in order that the recounting of the same corpuscles may be avoided. 

 A satisfactory procedure is to begin in the upper right-hand corner and proceed 

 from left to right counting the cells in each individual square. Take the next 

 lower row of squares and count from left to right and so on (see Fig. 101, page 

 311). Of course, all things being equal, the greater the number of squares ex- 

 amined the more accurate the count. It is considered essential under all cir- 

 cumstances, where an accurate count is desired, that the counting chamber 

 shall be filled, at least twice, and the individual counts made in each instance, 

 as indicated above, before the data are deemed satisfactory. Under no condi- 

 tions should less than 200 squares be examined. 



FIG. 97. ORDINARY RULING or THOMA-ZEISS COUNTING CHAMBER. (Da Costa.) 



To calculate the number of erythrocytes per cubic millimeter of 

 undiluted blood proceed as follows: Determine the number of cor- 

 puscles in any given number of squares and divide this total by the 

 number of squares, thus obtaining the average number of erythrocytes 

 per square. Multiply this average by 4000 to obtain the number of 

 erythrocytes per cubic millimeter of diluted blood, and multiply this 

 product by 100 or 200, according to the dilution, to obtain the number of 

 erythrocytes per cubic millimeter of undiluted blood. Thus : 



Average number of erythrocytes v v , x = Number of erythrocytes per 



per square cubic millimeter. 



Great care should be taken to see that the capillary pipette is prop- 

 erly cleaned. After using, it should be immediately rinsed out with the 

 diluting fluid, then with water, alcohol, and ether in the sequence given. 

 Finally dry air should be drawn through the capillary and a horsehair 

 inserted to prevent the entrance of dust particles. 



In counting leucocytes by means of the hemocytometer proceed as follows : 

 As mentioned above, if the diluting fluid is either Toison's or Sherrington's 



