2l6 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



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 calculation will 

 give the number of normoblasts per cubic millimetre. Thus, 

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

 blasts are seen whilst counting 500 leucocytes, the total number 



of normoblasts per cubic millimetre is '- '- — = 1,1 152. 



500 ' ^ 



2. Megaloblasts (Plate VIII., Figs. 10, 11, 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 

 'arger ; very large forms are called gigantoblasts, and may have 

 a diameter nearly three times as great as a normal corpuscle. 

 A megaloblast has a nucleus which is usually larger 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 overlooked. Except for this the only mistake 

 commonly made by beginners is to confuse a megaloblast with 

 polychromatophilic stroma (which frequently occurs) with a large 

 hyaline leucocyte. 



DIAGNOSTIC APPLICATIONS OF THE BLOOD- 

 COUNT AS A WHOLE 



In this chapter a brief outline of the chief practical applications 

 of the blood-count will be given, with especial reference to cases 

 where it is of use in the discrimination between two diseases 

 which are difficult to distinguish clinically. 



HEMORRHAGE. — After a severe haemorrhage there is at first no 

 alteration of the blood ; the total volume is diminished, but the 



