2/2 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



some seventy, and that this anaemia 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, not- 

 ing how many normoblasts you see whilst doing so. A simple 

 calculation will give the number of normoblasts per cubic 

 millimetre. Thus, if there are 8,000 leucocytes per cubic milli- 

 metre, and 72 normoblasts are seen whilst counting 500 

 leucocytes, the total number of normoblasts per cubic milli- 



72 x 8.000 



metre is -f- - = 1,152. 



500 



2. Megaloblasts (Plate VIII., Figs. 10, u, 12). The recog- 

 nition of these is of the utmost importance, as if they are 

 present in any appreciable numbers in the blood of an adult 

 the diagnosis of pernicious anaemia is almost a certainty, and 

 if a single example is found the diagnosis is highly probable. 

 They occur very rarely in adults in other conditions, but are 

 more common in severe anaemia in childhood, especially in 

 von Jaksch's anaemia, where they may be plentiful. 



In size megaloblasts resemble megalocytes, but may be even 

 larger; very large forms are called gigantoblasts, and may 

 have a diameter of nearly three times as great as a normal 

 corpuscle. A megaloblast has a nucleus which is usually 

 larg-er than that of a normoblast, though it may be smaller in 

 proportion to the size of the cell; it is sometimes double or 

 multiple. It stains much less deeply than the nucleus of a 

 normoblast in fact, it may stain so faintly that it is over- 

 looked. Except for this, the only mistake commonly made 

 by beginners is to confuse a megaloblast with polychromato- 

 philic stroma (which frequently occurs) with a large hyaline 

 leucocyte. 



