DIAGNOSTIC APPLICATIONS OF THE BLOOD-COUNT 283 



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 mild cases, and (2) very severe ones, usually rapidly fatal, 

 in which the system fails to react to the infection; the iodine 

 reaction of the leucocytes is well marked in these. A low 

 count in pneumonia, therefore, may be a good or bad sign : 

 which it is can be told by a glance at the patient. A moderate 

 leucocytosis which gradually declines is a bad sign in a case 

 of any severity. 



As a rule the leucocytes fall nearly to normal at the crisis, 

 sometimes a little before ; in such cases the crisis may be pre- 

 dicted, and a sudden fall to normal after a week or so is of 

 very good omen. If the leucocytes remain up after a crisis 

 it is most likely to be due to empyema. 



MALARIA. Here, of course, the diagnosis should be made 

 by finding the specific micro-organism in the blood (see 

 p. 189). Where this cannot be done the case may still be one 

 of malaria, and the blood-count may aid in the diagnosis. 

 There is anaemia, often coming on rapidly and attaining very 

 low figures. There is no leucocytosis, and according to many 

 observers there is a great increase in the large lymphocytes, 

 which almost always become more numerous than the small 

 ones. This test is not interfered with by the administration 

 of quinine, which renders the parasites difficult or impossible 

 to find. 



SCARLET FEVER AND MEASLES. In the former there is, ex- 

 cept in the very mildest cases, a marked leucocytosis; in the 

 latter the blood is normal in the absence of pneumonia or 

 other complications. In scarlet fever the leucocytes range 

 from 10,000 to 40,000, and according to some authors the 

 prognosis is very bad in cases showing more than 30,000; 

 there is an excess of polynuclears (80 to 90 per cent.), which 

 is very noticeable in children, where there is usually a high 

 proportion of lymphocytes. 



GERMAN MEASLES is not accompanied by leucocytosis. 



HOOPING-COUGH. There is a high grade of leucocytosis 

 (20,000 to 60,000), due mainly to an increase of lymphocytes. 



