236 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



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 

 anemia 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 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. 



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

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

 part that remains is normal. In a very short time, however, fluid 

 is absorbed from the tissues so as to make up the normal volume, 

 and in consequence the red corpuscles and haemoglobin fall in the 

 same proportion. With this there is usually a leucocytosis, high 

 figures (20,000 or more) being sometimes reached ; do not forget 

 this in dealing with a blood-count in a patient who has recently 

 had a haemorrhage. As the process of regeneration continues, the 

 improvement shows itself first in an increase of the red corpuscles, 

 so that the colour-index falls slightly (to about o'g). 



The anaemia from repeated haemorrhages is one of the varieties 

 of secondary anaemia. 



Secondary Anemia. — This term is used for anasmia which is 

 due to any definitely recognized cause — haemorrhage, malnutrition, 

 sepsis, intoxications (e.g., lead-poisoning), etc. — that is to say, it 



