ESTIMATION OF THE NUMBER OF LEUCOCYTES 193 



no light on the severity of the case, which must be estimated by 

 the amount of haemoglobin. 



3. In anaemia due to a single large haemorrhage the index is i 

 at first, both haemoglobin and corpuscles being, of course, lost in 

 equal proportions. As the blood begins to be regenerated it falls 

 somewhat, not usually lower than o-g. In ansemia due to multiple 

 haemorrhages, infectious diseases, poisoning, malnutrition, etc. 

 [secondary anamia), blood loss and regeneration are taking place 

 simultaneously, and the index falls to o-g, o-8, or even lower. 



ESTIMATION OF THE NUMBER OF LEUCOCYTES 



In clinical work it is quite sufficiently accurate to count the leuco- 

 cytes in the same preparation as was used for the red corpuscles, 

 and this is a great saving of time and trouble. Proceed as follows : 



Having focussed the rulings on the slide, move the draw-tube 



Fig. 48. — Showing Field of Microscope adjusted so that its Diameter 

 IS Equal to that of Eight Squares. 



of the microscope up and down until the upper and lower limits of 

 the field of the microscope coincide exactly with two of the hori- 

 zontal lines, and count the number of spaces (each enclosed between 

 two horizontal lines) in the diameter of the field. Using a ^-inch 

 objective it will be found possible to arrange matters so that these 

 are eight in number, and this will be found convenient, though any 

 other number will do. The essential thing is that the upper and lower 

 borders of the field shall coincide exactly with the rulings. We will 

 suppose that the number is eight. Then the diameter of the field 

 of the microscope is equal to eight times the length of a side of 

 a square, and its radius is equal to four times the length of a side 

 of a square. The total area of the field of the microscope is there- 



22 22 



fore 4 X 4 X — (»-2 X ;r, where iz is taken as -— ), or 50 and a frac- 



