218 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



centre of the slide C, a cover glass is gently laid on (so as to touch the drop, 

 which thus forms a layer i millimetre thick between the slide and cover 

 glass), and pressed down by two brass springs. In a few minutes the 

 corpuscles have sunk to the bottom of the layer of fluid, and rest on the 

 squares. The number on ten squares is then counted, and this multiplied 

 by 10,000 gives the number in a cubic millimetre of blood. The average 

 number of red corpuscles in each square ought therefore in normal human 

 blood to be 45-50. 



Differential counts to show the relative proportions of the varieties of 

 leucocytes are made in appropriately stained specimens. 



Oliver's Hgemacytometer. The following method, devised by Dr. George 



H;. r,:). Oliver's hiumucytomuter. 



