DIAGNOSTIC APPLICATIONS OF THE BLOOD-COUNT 245 



increase, or even a diminution, in an exhausted subject. If this 

 ■ rule is forgotten, the indications from the blood-count may be 

 unjustly stigmatized as misleading. 



Perforation. — There is a rapid increase of leucocytes, which is 

 said to occur in half an hour ; the total number may be 15,000 or 

 more. In a patient who is not greatly exhausted this is a very 

 sure sign ; exceptions do occur, but are not frequent. 



Hemorrhage. — If a count has been made a short time previously, 

 a fall in the red corpuscles may be noticed in some cases, but does 

 not seem always to occur. There may also be slight leucocytosis ; 

 this is only of importance in that it leaves the diagnosis of 

 perforation or haemorrhage doubtful, though raising the pre- 

 sumption that one or other has occurred. As a rule it is not 

 high, and the more it rises above 15,000, the more likely is 

 perforation to be the cause. 



Pneumonia. — When it occurs early in the disease there is usually 

 a slight leucocytosis ; when it occurs later there may be none. Do 

 not exclude pneumonia, therefore, because of its absence. 



It follows from the above that a raised leucocyte count in 

 typhoid fever always points to a complication of some sort, but 

 does not necessarily indicate its nature. 



Pneumonia. — Here the results of blood examinations are 



. fairly constant, and of much value in diagnosis and prognosis. 



In ordinary cases there is marked leucocytosis, due entirely to 



an increase of the polynuclears, which may reach 95 per cent. 



There is also moderate secondary anaemia. 



According to Ewing, who has had much experience on the 

 subject, the grade of leucocytosis is roughly proportionate to the 

 extent of the lesion. The following are his averages : 



Average Leucocytes. 



1 lobe affected 22,000 



2 lobes „ 22,700 



3 .. .. 25,000 



4 .. >. 27,000 



But higher counts, often much higher, are frequently seen. 



These figures serve to exclude typhoid fever, tuberculosis, 

 acute tuberculous pneumonia, and influenza, which do not cause 

 leucocytosis ; a true lobar pneumonia implanted on the latter 

 raises the leucocyte count, a lobular one does not usually do so. 



In a few cases of pneumonia there is no leucocytosis, but these 

 hardly detract from the value of the sign. They are (i) very 



