BLOOD EXAMINATION. 77 



Number of corpuscles per 1 c. mm. = 



No. of corpuscles x 4,000 x 100 (dil ution) 

 No. of squares. 



Normally the red blood cells number between 5,000,- 

 000 and 5,500,000 per c. mm. 



By this method of examination, information can also 

 be obtained of the size and shape of the red corpuscles. 



Estimation of White Corpuscles. The white cor- 

 puscles may be estimated at the same time as the red, 

 by counting at least 200 squares. 



It is better to estimate them separately, using the 

 large pipette of the haemacytometer. Blood is drawn 

 into this pipette up to 1 and then the bulb is 

 filled up to 11 with a .4% solution of acetic acid. The 

 acid destroys the red corpuscles leaving the white cells. 

 Examination is then made in the same manner as for 

 the red corpuscles. Normally there are on an average 

 10,000 white corpuscles per c. mm. 



The Haematocrit may also be used to determine 

 the numbers of red and white cells. The blood is drawn 

 into the graduated pipette and at once centrifuged, at 

 10,000 revolutions per minute, for 3 minutes. Normally 

 the red corpuscles will stand at 50 (on a scale of 100) so 

 that 1% =100,000 corpuscles. To calculate the number 

 of red corpuscles one simply adds five ciphers to the 

 percentage reading. The leucocytes are found on the 

 surface of the red discs, as a narrow white band. Any 

 increase in their numbers will be detected by an in- 

 crease of this band. 



