50 TROPICAL MEDICINE AND HYGIENE 



well-made films, either fresh, or preferably stained by 

 Leishman's method, the parasites can be found usually 

 with little difficulty. The essential is that the films, 

 whether wet or dry, are so spread that in considerable 

 portions of the film the corpuscles are lying flat and 

 separate from one another. 



The evidences of malaria derived from blood examina- 

 tions are : 



(1) Discovery of parasites. This is conclusive, but 

 in persons who have been taking quinine the non- 

 discovery does not prove that the patient has not got 

 malaria. In the intervals between attacks of fever, 

 whether after treatment or naturally, a prolonged search 

 may be necessary before the parasites are found. 



(2) Pigmented leucocytes, usually the large mono- 

 nuclear or hyaline leucocytes. These are conclusive of 

 recent malaria. They are often very scanty, so that it 

 is only rarely that they aid in the diagnosis unless a 

 prolonged search be made. 



(3) Increase in the relative proportion of the large 

 mononuclear leucocytes, without any increase in the 

 total number of leucocytes. In malaria and for a 

 variable period after malaria the proportion of large 

 mononuclear leucocytes is raised to 15 per cent, or 

 even more. This change is not affected by the adminis- 

 tration of quinine, and is more marked when there is no 

 pyrexia. It is therefore of great value in just those 

 cases of malaria in which the parasites are not to be 

 found. It does not, however, prove that the malaria is 

 still present, as the change is so persistent, but, as a rule,, 

 it indicates past malaria. If there is a coexisting disease 

 such as pneumonia, sepsis, or even acute hepatitis, which 

 produces an increase in the number of polymorpho- 

 nuclear leucocytes, this change will completely mask the 

 mononuclear increase of malaria in a differential count. 

 In children it is of less value, as in them an increase in 

 the large mononuclear leucocytes is fairly common with- 

 out any disease. 



