424 



THE BLOOD 



[CH. XXVI. 



Gowers' Hcemacytonwter consists of a small pipette (A), which, when filled up 

 to a mark on its stem holds 995 cubic millimetres. It is furnished with an india- 

 rubber tube and glass mouth-piece to facilitate filling and emptying ; a capillary 

 tube (B) marked to hold 5 cubic millimetres, and also furnished with an indiarubber 

 tube and mouth-piece ; a small glass jar (n) in which the dilution of the blood is 



FIG. 356. 



J TTL 



FIG. 357. 



performed ; a glass stirrer (E) for mixing the blood and salt solution thoroughly ; 

 (F) a needle, the length of which can be regulated by a screw ; a brass stage plate 

 (c) carrying a glass slide, on which is a cell one-fifth of a millimetre deep, and the 

 bottom of which is divided into one-tenth millimetre squares. On the top of the 

 cell a cover-slip rests. A standard saline solution of sodium sulphate, or similar 

 salt, of specific gravity 1025, is made, and 995 cubic millimetres are measured by 

 means of the pipette into the glass jar, and with this 5 cubic millimetres of blood, 

 obtained by pricking the finger with the needle, and measured 

 in the capillary pipette (B) are thoroughly mixed by the glass 

 stirring-rod. A drop of this diluted blood is then placed in the 

 cell and covered with a cover-slip, which is fixed in position 

 by means of the two lateral springs. The layer of diluted 

 blood between the slide and cover-glass is one-fifth of a milli- 

 metre thick. The preparation is then examined under a 

 microscope with a power of about 400 diameters, and focussed 

 until the lines dividing the cell into squares are visible. 



After a short delay, the red corpuscles which have sunk 

 to the bottom of the cell, and are resting on the squares, are 

 counted in ten squares, and the number of white corpuscles 

 noted. By adding together the numbers counted in ten (one- 

 tenth millimetre) squares, and, as the blood has been diluted, 

 multiplying by ten thousand, the number of corpuscles in one 

 cubic millimetre of blood is obtained. The average number 

 of corpuscles per cubic millimetre of healthy blood, according 

 to Vierordt and Welcker, is 5,000,000 in adult men, and 

 4,500,000 in women ; this corresponds to an average of 50 and 

 45 corpuscles respectively per square of Gowers' instrument. 



A haemacytometer of another form, and one that is much 

 used at the present time, is known as the Thoma-Zeiss haema- 

 cytometer. It consists of a carefully graduated pipette, 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 1 (fig. 357) the saline solution may 

 afterwards be drawn up the stem to the line 101 ; in this way 

 we have 101 parts, of which the blood forms 1. As the con- 

 tents of the stem can be displaced unmixed we shall have in 

 the mixture the proper dilution. The blood and the saline so- 

 lution are well mixed by shaking the pipette, in the bulb of 

 which is contained a small glass bead for the purpose of aid- 

 ing the mixing. The other part of the instrument consists of 

 a glass slide (fig. 356) upon which is mounted a covered disc, 

 w, accurately ruled so as to present one square millimetre 

 divided into 400 squares of one-twentieth of a millimetre each. The micrometer 

 thus made is surrounded by another annular cell, c, which has such a height as to 

 make the cell project exactly one-tenth millimetre beyond m. If a drop of the 

 diluted blood is placed upon m, and c is 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 T T , will be T7 fri> of a cubic millimetre. An average of ten or more 



FIGS. 856 and 857. 



Thoma-Zeiss 

 Hsemacytometer. 



