212 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



recorded, and the average is about 0-5. The exact 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 o'g. In anaemia due to multiple 

 haemorrhages, infectious diseases, poisoning, malnutrition, etc. 

 (secondary ancemia), 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 

 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 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 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 microscope 



22 22 



is therefore 4 x 4 x — {r^xir, where it is taken as — ) , or 50 and 



a fraction. 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. The slide is then moved on 

 until a perfectly fresh portion of the field comes into view ; it is 

 advisable to go too far rather than not far enough. For this 



