MEASUREMENT OF SPERM MOTILITY 



43 



depth of focus, (3) variation in cell length, and (4) passage off center 

 of the aperture. With these factors in mind, the standard value of / 

 adopted for interpreting the recordings was 



/ = 64 /* 



without taking into account the slight dependence of / on v . 



For the rotating cells, which satisfy statistical sampling conditions, 



n dv 



f(v)dv 



where n v is the number of cells with velocities between v and v + dv 

 passing the aperture per second, and f(v) is the velocity distribution 

 of the sample. By recording passages over a long time interval, the 

 velocity distribution and, thus, the mean velocity are obtained. Fig- 

 ure 1 1 shows the mean velocity obtained in this way versus the mean 

 velocity determined from films taken on the same slide immediately 

 after the photoelectric measurement was complete. An accuracy for 

 measuring v of about 4% is obtained. 



100 



£ 



50 



50 100 



V PHOTOELECTRIC, Lim/SEC. 



Fig. 11. Mean velocity of sperm samples measured photoelectrically 

 and by means of films. 



