43 



Leucocytic Variation. Often in cases where pig- 

 mented leucocytes are difficult to find there is a very 

 obvious increase in the percentage of the large mono- 

 nuclear leucocytes. This change, which is usually very 

 pronounced in the apyretic periods of an attack of 

 malaria, is, however, most frequently absent during 

 pyretic periods. If, during a period of low tempera- 

 ture, this change is not found, there is a strong pre- 

 sumption that the case is not malarial. If the blood 

 be taken at the height of the fever, a negative result 

 does not exclude malaria, and a further examination 

 should be undertaken, if possible, during an apyretic 

 period. In some cases the change can be detected 

 even during the pyretic periods, but in these it is 

 always more marked in the apyretic. In some cases, 

 during the course of the fever, no such change occurs, 

 but appears immediately the temperature subsides, 

 and diminishes as convalescence proceeds. Perhaps 

 the cases where this test is of the greatest value are 

 those where the patient has already been treated with 

 quinine, and one can scarcely hope, even if the disease 

 be malaria, to find parasites in the blood. 



From the results obtained by blood counts of a 

 considerable number of Europeans living in the tropics, 

 we found that an increase beyond fifteen per cent, of 

 the large mononuclear forms is proof of an actual or 

 recent malarial infection, whereas with a value of 

 twenty per cent, it is almost always possible, by long 

 search, to find an occasional parasite or pigmented 

 leucocyte. A value of over twenty per cent, probably 

 implies actual infection at the time of observation. 



