IV 



THE BLOOD: FOKMED CONSTITUENTS 



103 



pricking the finger with a needle. A column of blood is aspirated by means 

 of the rubber tube to division 0'5 or 1 of the pipette, and after quickly 

 drying the lower end, the bulb of the pipette is filled up to the figure 101 

 (which expresses its capacity in c.niin.) with 3 per cent salt solution, or with 

 Paciiii's fluid as modified by Hayem and Gram (corrosive sublimate 0*5 grm., 

 sodium sulphate 5 grins., sodium chloride 2 grins., distilled water 

 200 grins.)- It is then sufficient to shake the pipette for a few 

 moments in order that the glass ball (), which is loose inside 

 the bulb, may mix the blood with the salt solution, and make 

 the fluid homogeneous. As the division 0'5 corresponds exactly 

 to -^-B- of the total capacity of the bulb, and the figure 1 

 exactly to T -j-jj-, we know that the mixture obtained is in the 

 ratio of 1 : 200 or 1 : 100. 



The counting is done upon a carrier (II) of thick glass 

 with a groove (6), the bottom of which is divided by lines cut 

 with a diamond into 400 minute squares (as is shown in III). 

 Into this groove, the capacity of which is O'l c.mm., a drop of 

 the blood solution contained in the bulb of the pipette is. intro- 

 duced, care being taken to drive out the liquid contained in the 

 capillary portion, which has not been mixed with the blood. 

 When the drop is placed in the groove, a cover glass (a) is 

 quickly applied, and after letting the preparation rest for a few 

 minutes upon a perfectly horizontal surface, in order that the 

 red corpuscles may be spread evenly upon the floor of the groove, 

 the counting is undertaken under a magnification of 200 



II 



FIG. 30. Thoina-Zeiss Haemacytometer. I, Graduated pipette (Potain's mixer); II, cell for 

 counting corpuscles, side view ; III, squared divisions of bottom of haeuiacytometer. 



diameters. The number of the corpuscles counted is divided by the number 

 of squares examined, which should never be less than 200 ; thus obtaining 

 the average of the red corpuscles contained in each square, which represents 

 T1J j !n5 . c.mm. Hence, if we wish to know the number of corpuscles in c.mm. 

 it is only necessary to multiply the number found first by 4000, and then 

 by 100 or 200, according as the blood has been diluted 100 or 200 times. 

 To take a practical example : If 1225 corpuscles are counted in 250 squares, 

 VOL. I H b 



