102 PROBLEMS OF FERTILIZATION 



and each was tested for fertilization power at the ages 

 given by adding i drop of sperm to 5 drops of eggs in 

 10 c.c. of sea-water. Such sperm suspensions when 

 perfectly fresh will fertilize 100 per cent of eggs when 

 so used. The table shows that the fertilizing power 

 falls off with age in inverse proportion to concentration. 

 This is in inverse relation to activity and to CO 2 and 

 H ion concentration. The last point was demonstrated 

 by measurements of the rate of increase of H ion concen- 

 tration in sperm suspensions of varying concentration, 

 which runs parallel with the longevity. 



In spite of the more rapid rate of increase in H ion 

 concentration with sperm concentration Cohn was able 

 to show that the amount of CO 2 produced per unit of 

 sperm is ultimately the same in more concentrated and 

 in more dilute suspensions; the difference is merely in 

 the rate of combustion, which is more rapid in propor- 

 tion to activity. The more dilute suspensions use up 

 their available store of energy more rapidly, the more 

 concentrated suspensions less rapidly. 



b) Aggregation and chemotaxis. We have seen that 

 fresh active sperm suspensions of Nereis rapidly form 

 dense aggregations (p. 95, Fig. 13) in masses. Under 

 a low power of the microscope each mass appears like a 

 swarm of bees, owing to intense rotary activity of the 

 peripheral spermatozoa. But those in the interior of 

 the dense mass must be quiescent. The reaction is 

 dependent on the existence of a certain H ion concentra- 

 tion of the sea-water, for if the sea-water be rendered 

 hyperalkaline the aggregations do not form, however 

 intense the activity of the spermatozoa. The reaction 

 is in fact due to rapid CO 2 production by the sper- 



