DIFFERENTIAL LEUCOCYTE COUNT 235 



plentiful. Except where this occurs it is not of much diagnostic 

 importance, unless it is true that it occurs as a very early and 

 constant sign in lead-poisoning. 



Nucleated Forms (-blasts). 



I. Normoblasts (Plate VIII., Figs. 7, 8, 9).— These are corpuscles 

 which resemble the normal in shape and size, but which have a 

 nucleus. This is central, large in proportion to the corpuscles, 

 surrounded by a comparatively narrow band of stroma, and 

 circular ; in some cases it is double or multiple. Normoblasts can 

 usually be recognized with ease from any other cells which occur in 

 the blood, from the fact that the nucleus stains very deeply — more 

 deeply than any other found in the blood. It frequently happens 

 that the narrow ring of stroma may show polychromatophil de- 

 generation and stain blue ; in this case it is difficult to distinguish 

 the cell from a lymphocyte, but the deeply stained, almost black, 

 nucleus should prevent mistakes. 



Normoblasts are the cells from which the normal blood- 

 corpuscles are formed, but in health they are confined to the 

 bone-marrow, except in very young infants, in whom a very few 

 may be found in the circulation. Their presence in the blood of 

 older persons indicates that there is an anaemia of some severity, 

 and that this anasmia is being combated in a normal way ; the 

 bone-marrow is so active that some of its normoblasts overflow 

 into the circulating blood. They are therefore rather a good sign 

 than otherwise. Occasionally you may find them in very large 

 numbers in the blood of a case of anaemia, especially in chlorosis : 

 this is called a " blood-crisis," and when it occurs the patient will 

 improve very rapidly. If you want to count their numbers, the 

 simplest way is as follows : Count the leucocytes in the way 

 already described, and calculate the number per cubic millimetre. 

 Then take a stained film and count 400 or 500 leucocytes, noting 

 how many normoblasts you see whilst doing so. A simple calcu- 

 lation will give the number of normoblasts per cubic millimetre. 

 Thus, if there are 8,000 leucocytes per cubic millimetre, and 72 

 normoblasts are seen whilst counting 500 leucocytes, the total 



1 r ,1 1 ■ -.I- • 72 X 8,000 



number oi normoblasts per cubic milhmetre is = 1,152. 



^ 500 ' -^ 



2. Megahhlasts (Plate VIII., Figs. 10, ii, 12). — The recognition 



of these is of the utmost importance, as if they are present in any 



