Ill] 



HUMAN BLOOD CORPUSCLES. COUNTING 



25 



7. Enumeration of the red corpuscles. Count the number of 

 red corpuscles with a Thoma hsemacytometer (Fig. 1). 



In this the capillary tube (t) (Fig. 1. A), up to the mark 1 

 contains T ^th of the bulb (6) between the marks 1 and 101. 

 On the disc (d) (Fig. 1. B), 1 square millimetre is divided into 

 400 squares, each -^ih mm. The piece of glass (e) around this 

 disc is j^th mm. above it. Thus when the cover-slip is put on, 

 the space between each square and the cover-slip is 



cubic mm - 



See that the counting cell and the pipette are clean and have 

 ready a large cover-slip and a watch-glass containing Hayem's 

 fluid, which consists of 1 part of sodic chloride, 5 parts of 

 sodic sulphate, '5 parts of corrosive sublimate in 200 parts of 

 water. 



Fig. 1. 



Prick the finger 1 and when a sufficiently large drop of blood 

 is obtained, gently suck blood into the pipette as far as the mark 



1 The prick of a needle does not readily give sufficient blood ; it 

 is best to use the triangular needle or shielded lancet made for the 

 purpose, and to thrust it suddenly into the finger. In obtaining blood 

 from another person it may be obtained from the ear, as it is less 

 sensitive than the finger but sufficiently vascular. 



