DIFFERENTIAL LEUCOCYTE COUNT 269 



Mast Cells. These only occur in fractional percentages in 

 any disease, except myeloid leucocythaemia, where 5 or 10 per 

 cent, is common; this is perhaps the most definite, constant, 

 and readily recognized sign of the disease. The large forms, 

 with circular or kidney-shaped nuclei, are practically only 

 seen in this condition. 



MORPHOLOGICAL CHANGES IN THE RED CORPUSCLES. 



Normal red corpuscles (Plate VIII., Fig. i) hardly need 

 description, and the practitioner can readily make himself 

 familiar with their appearance. They are strongly oxyphile, 

 staining pink with the eosin in Jenner's stain, and with acid 

 fuchsin in the triacid. It is especially important to become 

 familiar with their sise t since modifications in this respect are 

 very important in the diagnosis of certain forms of anaemia. 



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 de- 

 signations, have names terminating- in -cyte (microcyte, mega- 

 locyte, etc., based on the type of the normal corpuscle, which 

 is called erythrocyte, xanthocyte, or normocyte, 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 VIII., 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 recognition is not a matter of much importance. 



2. Megalocytes or Macrocytes (Plate VIII., 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 



