THE PERCENTAGE OF CORPUSCLES AND PLASMA 



135 



fication, by the division of the cell area into squares of known size. Having 

 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 

 equalling 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 shaking the pipet, in 

 the bulb of which is contained a small glass bead for 

 the purpose of aiding the mixing. The other part of 

 the instrument consists of a glass slide, figure 130, upon 

 which is mounted a covered disc, m, accurately ruled 

 so as to present one square millimeter divided into 400 

 squares of one-twentieth of a millimeter each. The 

 micrometer thus made is surrounded by another annu- 

 lar cell, c, which has such a height as to make the cell 

 project exactly one-tenth millimeter beyond m. If a 

 drop of the diluted blood be placed upon w, and c be 

 covered with a perfectly flat cover-glass, the volume of 

 the diluted blood above each of the squares of the mi- 

 crometer, i.e., above each 4^-0", will be 4-0 ~o of a cubic 

 millimeter. An average of ten or more squares is then taken, and this num- 

 ber multiplied by 4000 X 100 gives the number of corpuscles in a cubic 

 millimeter of undiluted blood. A separate pipet is used for making dilu- 

 tions for counts of leucocytes. In this, the dilution is made of one part of 

 blood and ten parts of diluting fluid. Acetic acid, 0.2 of one per cent, is 

 usually employed for this purpose. 



5. The Percentage of Corpuscles and Plasma in Human Blood. 

 Fill the two graduated capillary tubes of a hematocrite with blood drawn 

 from the tip of your own finger, insert into the instrument, and centrifuge as 

 rapidly as possible. The experiment must be performed within the time 

 limit of clotting in order to be successful. The corpuscles will be thrown 

 down and the percentage of plasma and corpuscles can be read off directly. 

 Should one fail to fill the tube exactly full, then the percentage of plasma and 

 corpuscles can be calculated from the proportion which each bears to the 

 quantity in the tube, 



FIG. 131. Thoma- 

 Zeiss Hemacytometer, 

 pipet. 



