THE NUMBER OF CORPUSCLES 



159 



corpuscles in a measured length of the tube or in a given area of the cell 

 is counted. The length of the tube and the area of the cell are ascertained 

 by means of a micrometer scale in the microscope ocular; or, in the case of 



Depth 



0.100mm 



4OO 



DOME NH'BAIER RULING 



FIG. 130. Section of the new Bausch and Lomb form of the Thoma-Zeiss Hemacy- 

 tometer. This form has the advantage of having the two standard graduated scales 

 reproduced in the next figure ground in the glass slide itself. 



Gowers's modification, by the division of the cell area into squares of known 

 size. Haying ascertained the number of corpuscles in the diluted blood, it 

 is easy to find out the number in a given volume of normal blood. 



The hemacytometer, which is most used at the present time, is known 

 as the Thoma-Zeiss hemacytometer. It consists of a 

 carefully graduated pipet, in which the dilution of the 

 blood is done; this is so formed that the capillary stem 

 has a capacity equaling one-hundredth of the bulb above 

 it. If the blood is drawn up in the capillary tube to 

 the line marked i, figure 131, the saline solution may 

 afterward be drawn up the stem to the line 101 ; in 

 this way we have 101 parts of which the blood forms i. 

 As the content of the stem can be displaced unmixed we 

 shall have in the mixture the proper dilution. The 

 blood and the saline solution are well mixed by shak- 



Neubauer Ruling Fuchs-Rosenthal Ruling 



FIG. 1300. Standard hemacytometer rulings, 1/400 square 

 millimeter. 



FIG. 131. Thoma- 

 Zeiss Hemacytome- 

 ter, pipet. 



ing the pipet, in the bulb of which is contained a small glass bead for the 

 purpose of aiding the mixing. The counting instrument consists of a glass 

 slide, figure 130, provided with a depressed area the surface of which is 



