THE PHYSIOLOGY OF FERTILIZATION 



135 



The fertilizing power of sperm suspensions may be 

 expressed in curves whose ordinates are percentages of 

 fertilization, and the abscissae a geometrical series of 

 dilutions of i per cent sperm in powers of 2. This 

 method was adopted for the abscissae because of the 

 method of successive half-dilutions used in many experi- 

 ments, and because the enormous range of fertilizing 

 power made it impossible to compare results on one 



FIG. 16. Curve of fertilizing power of perfectly fresh sperm 

 suspensions of A rbacia. The ordinates give percentages of eggs fertilized. 

 The abscissae represent dilutions of the sperm in powers of 2, viz.: 



scale with an arithmetical progression. When it is 

 realized that fertilizing power may extend to 1/90,000,- 

 ooo of i per cent the necessity of the geometrical series 

 in the abscissae will become apparent. 



Figure 16 is prepared from data of experiments calcu- 

 lated to bring eggs and sperm together in the freshest 

 possible condition of the sperm. In general measured 

 quantities of washed eggs were put in measured amounts 

 of sea-water, and measured quantities of definitely cali- 

 brated sperm suspensions added and stirred in as uni- 

 formly as possible. A control of unfertilized eggs in 



