MEASUREMENT OF SPERM MOTILITY 



35 



FOCAL DISTANCE,(inn 

 Fig. 3. Width of the image of the tail of a sperm cell as a function of 

 the distance to the plane of focus. Width expressed in microns (^ and ^m 

 employed interchangeably in figures throughout paper). 



covered during consecutive intervals of 0.5 sec, is constant within 4% 

 (standard deviation) during the time the cells can be observed before 

 leaving the field of view. The "orbits" of the cells are fairly straight; 

 of 150 cells measured, 92 had a radius of curvature of the orbit r > 

 1 mm, 36 had 1 < r < 0.5 mm, and the rest r < 0.5 mm. The im- 

 plication of this is that for statistical measurements, the velocity of 

 a sperm and also the velocity distribution of a sample are useful 

 concepts, and that random samples of the moving cells can be ob- 

 tained. 



The velocity turns out to be proportional to the frequency of rota- 

 tion (Fig. 4). If we write: 



*=*•/«* (1) 



the constant p represents the pitch of the helical movement of the 

 head. For the ejaculate represented in Fig. 4, mean and standard 

 deviation of p are: p = 12.6 ± 2.4 microns. From seven ejaculates* 

 it was found that: 



H.9 ± 0.7 



Even though the tail wave cannot be expected to be sinusoidal or to 

 have a constant amplitude as it progresses along the tail (Machin, 

 1958), an average value for the amplitude can be measured, so long 

 as the tail, at the moment the data are taken, is "parallel" to the slide 



* Most of these data were obtained by the method of dark field-track photog- 

 raphy, as introduced by Rothschild (1953b). This procedure saves considerable 

 time needed for analysis. 



