differential leucocyte count 233 



Abnormal Forms of Red Corpuscles. 



Two great classes are to be recognized— those which retain 

 the characters of a normal red corpuscle, in that they have no 

 nuclei, and those which resemble the embryonic corpuscles in 

 being nucleated. The former, where they have special designa- 

 tions, have names terminating in -cyte (microcyte, megalocyte, 

 etc., based on the type of the normal corpuscle, which is called 

 erythrocyte, xanthocyte, or pormocyte, convenient terms that 

 have never gained wide currency), whilst the nucleated forms 

 have names ending in -blast. 



Abnormal Non-nucleated Forms (-cytes). 



1. Microcytes (Plate VIIL, Fig. 4) are red corpuscles which are 

 decidedly below the normal in size, but are otherwise normal. 

 They are indications of anaemia, but, as they may occur in any 

 severe anaemia, and do not serve to indicate its type, their recog- 

 nition is not a matter of much importance. 



2. Megalocytes or MacrocyUs {PlaXe VIIL, Fig. 5). — These are 

 large corpuscles, and the name should be restricted to forms 

 that are at least one and a half times as broad as a normal 

 corpuscle ; they may be much larger. 



It is important to learn to recognize them, since their presence 

 is an almost constant sign of pernicious anaemia, and it is rare 

 to find them in any considerable numbers in other conditions. 

 When you are frequently examining blood-films with the same 

 lens and eye-piece, you will soon be able to pick out forms of 

 abnormal size. When you have not- had this experience it is 

 advisable to make a film of normal blood for comparison, and to 

 look first at one and then at the other. A still better method 

 (due to Shattock) is to mount the two films (the normal and 

 abnormal, both stained) face to face, and then to mount the pair 

 on a slide, and examine them with an oil-immersion lens ; a slight 

 turn of the fine adjustment will enable you to pass at once from the 

 one to the other, and to compare the diameters of the corpuscles 

 with some degree of accuracy. Another useful method is to 

 employ the counting-chamber of the haemocytometer, and an 

 idea of the diameter of the reds should be gained in all cases of 

 pernicious anaemia whilst the count is being made. The diameter 

 of one of the small squares is almost exactly six times that of a 



