41 



already been treated with quinine, and one can 

 scarcely hope, even if the disease be malaria, to 

 find parasites in the blood. 



To Make a Differential Count of the 

 Leucocytes 



Large films are necessary, especially .in 

 malaria where, during the apyretic period, there 

 is a distinct diminution in the total number of the 

 white cells. It is important, in making films for 

 leucocyte counting, that the margins and terminal 

 points of the film' be regular, and so in a 

 convenient position for examination (Fig. i). 

 The margin of the film is focussed and passed 

 beneath the objective. By passing along one- 

 half or the whole of the margin of the film, the 

 great majority of the leucocytes in the film are 

 seen. In order to obtain accurate results, one 

 thousand leucocytes should be counted, but a 

 count of three or four hundred is generally suffi- 

 cient for diagnostic purposes. Counts of a smaller 

 number of leucocytes are valueless, as too great 

 variations will occur. 



As a leucocyte is seen, it is marked under the 

 heading, large mononuclear, intermediate, transi- 

 tional, small mononuclear, polynuclear, eosinophil, 

 as the case may be. As many as ten to twenty 

 or more are mentally noted before making each 

 record in its column. 



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 



