BY K. GKEIG-SMITH. G95 



misleading results. But while the time may not be shortened, 

 the counts may be rendered more representative by taking 

 advantage of several points which have been indicated. Thus the 

 corpuscular "separate" may with decided advantage replace the 

 leucocyte "cream."* 



The need for uniformity of work has been shown by the neces- 

 sity for always taking the first drop blown out from the capillary 

 pipette in preparing the smears. The necessity for mixing the 

 suspensions a definite number of times and for always counting 

 the same portion of the smears has been indicated. When the 

 room-temperature is above 12°C., the sealed capillary tubes con- 

 taining the mixed serum and suspensions should be incubated 

 immediately after mixing and the smears should be made upon 

 the withdrawal of the pipette from the incubator. 



When using the "separate," one meets few leucocytes with 

 relatively high numbers, and when one does my experience has 

 been that they should be included. There may be a high number 

 in the first 50 cells, but the chances are that in the second 50 

 there are two or more moderately high numbers that balance the 

 high count of the first 50. It appears to make little difference 

 whether or not the zeros are included, for in a series of tests such 

 as have continually been made in this research, the zeros in each 

 duplicate test have been approximately equal. I have noted a 

 divergence in some instances, and am therefore in favour of 

 including the zeros in the counts. I have tried various methods 

 of obtaining a phagocytic index, such as by taking the average 

 of the fiftieth and fifty-first cells, of the middle 80, 60, 40 and 20, 

 but have always found them to be misleading. The only method 

 that can be trusted is the usual one of counting 100 or more 

 leucocytes and taking the average per leucocyte. It is advisable 

 to have the bacterial suspension of such concentration that about 

 five bacteria are ingested by the average leucocyte under the 

 conditions of the experiment. 



* According to Fleming (Practitioner, 1908) the use of the "cream " has 

 been abandoned, and a uniform suspension of the total corpuscles is. 

 employed. 



