DIAGNOSTIC APPLICATIONS OF THE BLOOD COUNT 237 



includes all cases of anaemia except those of unknown pathology, 

 such as chlorosis and pernicious anaemia. 



In secondary anaemia there is a reduction of red corpuscles to 

 an extent dependent on the potency and continuance of the cause, 

 and a slightly greater reduction of the haemoglobin, so that the 

 colour-index is lowered. It does not usually fall below 07, 

 and o"8 may be taken as a fair average. Anything below this is 

 rarely met with apart from chlorosis. The red corpuscles are 

 usually practically normal in appearance ; normoblasts are rare, 

 and their presence is a good sign. 



The leucocytes, especially the polynuclears, are usually slightly 

 increased, and this is the chief or only means of distinguishing a 

 secondary anaemia with low colour-index from chlorosis, in which 

 the leucocytes are normal or reduced. 



Pernicious Anaemia. — The feature which usually first raises 

 suspicion of pernicious anaemia is the high colour-index. It is 

 usually over i, and, taking the average of a number of cases, 

 it increases in proportion to the amount of reduction of the 

 corpuscles, thus : 



When you find a case with a high colour-index, it should 

 immediately raise a suspicion of pernicious anaemia. Turn 

 again to the preparation in which you have counted the reds in 

 the Thoma-Zeiss haemocytometer, and look for unusually large 

 corpuscles (megalocytes), which, according to Ewing, should form 

 35 per cent, of all corpuscles, or the diagnosis is to be made with 

 caution. Then count the leucocytes in the same preparation. 

 Leucopenia is very characteristic ; if the number exceeds 6,000, 

 pernicious ansmia is unlikely, unless inflammatory complications 

 are present. Then make a differential count on a stained film, 

 looking out for megaloblasts and normoblasts as you do so ; in 

 pernicious anaemia there is almost always a relative lymphocytosis, 



