246 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



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 (p. 162). 

 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, except 

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

 blood is normal in the absence of pneumonia or other complica- 

 tions. 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. This is said 

 to occur before the hooping occurs and to be of diagnostic value, 

 but leucocytosis with lymphocytosis is so common in children 

 that little value should be attached to it unless really high figures 

 are found. 



Influenza. — Here the blood-count may be of value, since, in 

 contradistinction to the majority of acute febrile diseases, there 

 is no leucocytosis if complications are absent. In other febrile 

 diseases of rapid onset — pneumonia, tonsillitis, rheumatic fever, 

 septic affections, plague, etc. — leucocytosis is almost constant. 



