248 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



figure throws 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 0*9. 

 In anaemia due to multiple haemorrhages, infectious diseases, 

 poisoning', malnutrition, etc. (secondary anamia), blood loss 

 and regeneration are taking place simultaneously, and the 

 index falls to 0-9, o - 8, or even lower. 



ESTIMATION OF THE NUMBER OF LEUCOCYTES 



In clinical work it is quite sufficiently accurate to count 

 the leucocytes 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 of the microscope up and down until the upper and 

 lower limits of the field of the microscope coincide exactly 

 with tw r o of the horizontal lines, and count the number of 

 spaces (each enclosed between two horizontal lines) in the 

 diameter of the field. Using a J-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 num- 

 ber is eight. Then the diameter of the field of the micro- 

 scope 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 is therefore 



22 22 



4 x 4 x (r* x TT, where TT is taken as ), or 50 and a frac- 

 tion. Practically, therefore, when we look down the micro- 

 scope after it has been adjusted in this way we are looking 

 at fifty squares; and this fact enables us to dispense entirely 

 with the rulings, and count over the whole area of the 

 disc with great rapidity. The slide is placed in position, and 

 all the cells which are seen in the field counted and the 

 result noted down, or, preferably, dictated to someone else. 



