Orv^ 

 raelct 



UO^. 



\\.t\a,eeJroc toxxXt-t 



The ruling of the Turck disc. Explanation of the squares. In 

 the first place, we have the square which incloses the entire ruled sur- 

 face. This is made up of nin? squares each i mm. square. These are 

 the squares to use in connection with leukocyte counts with the white 

 pipette. They may be termed the large squares. The very smallest 

 square which can be found are those made by the intersection of the 

 double-ruled lines in the center; they are 1/40 mm. square and are 

 never used for any purpose. When we refer to the small square, 

 those which are found in groups of sixteen bounded by double-ruled 

 lines are intended. These squares are 1/20 mm. square and are used 

 in the count of red cells. Another square is outlined in the more 

 sparsely ruled large square in each of the four corners. This square 

 includes a space equal to sixteen small squares and in addition the 

 spaces in the frame-like space surrounding make twenty additional 

 small squares, cr thirty-six in all. This space is not used ordinarily. 

 DaCosta uses a space made up of the sixteen small squares and the 

 bordering upper and left-hand double-line cells. This gives twenty- 

 five small squares. 



There are 400 small squares in each large square, consequently as 

 there are nine large squares the entire ruled surface consists of 3600 

 small squares. 



