THE PERCENTAGE OF CORPUSCLES AND PLASMA 



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 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 W T C shall have in the mixture the proper dilu- 

 tion. 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 milli- 

 meter divided into 400 squares of one-twentieth of a 

 millimeter each. The micrometer thus made is sur- 

 rounded by another annular 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 m, and c be covered with a perfectly flat 

 cover-glass, the volume of the diluted blood above each 

 of the squares of the micrometer, i.e., above each ffa, 

 will be :nnnr f a cubic millimeter. An average of 

 ten or more squares is then taken, and this number multiplied by 4000 X 

 100 gives the number of corpuscles in a cubic millimeter of undiluted blood. 

 A separate pipet is used for making dilutions for counts of leucocytes. In 

 this, the dilution is made of one part of blood and ten parts of diluting fluid. 

 Acetic acid, o. 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. 



6. Estimation of the Percentage of Hemoglobin. The per cent, of 

 hemoglobin in a sample of blood can be obtained by the instrument known 



Zeiss Hemacytome- 

 ter, pipet. 



