STUDIES IX THE PHYSIOLOGY OF SPERMATOZOA. 175 



end of the suspension; now become the positive pole. There 

 they are again inactive. In the more alkaline part of the sus- 

 pension the sperm are extremely active. Frog sperm (Lillie, 

 R. S., 1903) and Echinid sperm (Gray, J., 1915) behave in a 

 similar manner. This phenomenon does not occur if sperm 

 are first inactivated by an increase in the hydrogen ion concen- 

 tration of the suspension (Gray, J., 1915). 



OXYGEN AND CARBON DIOXIDE CONCENTRATION. 



Similar in kind is the observation of Buller (Duller, A. H., 

 1902) that when a bubble of oxygen is incorporated in a sus- 

 pension of Echinus sperm those in the immediate vicinity of the 

 oxygen remain active after the sperm at a greater distance " have 

 all come to rest from want of oxygen." Between the active 

 sperm and the inactive sperm there is a zone "in which there are 

 comparatively very few spermatozoa." The active sperm 

 gradually traverse the clear zone "and collect on the inner edge 

 of the zone" (of inactive sperm) "upon reaching which they 

 cease to move. A ring of thickly placed, dead spermatozoa thus 

 arises" (Buller, A. H., 1902, p. 158). The spermatozoa were 

 not "dead" but merely inactive in a region of low oxygen and of 

 high carbon dioxide concentration. 



F. R. Lillie has observed the converse phenomenon. He in- 

 jected a drop of sea water with a carbon dioxide concentration 

 of approximately I per cent, into a suspension of Nereis sperm 

 (the sperm of Arbacia are not so sensitive to carbon dioxide but 

 "the reactions of Arbacia spermatozoa are essentially the same 

 in principle as those of Nereis") (Lillie, F. R., 1913, p. 546) and 

 noticed that a ring of sperm is formed at a definite concentration 

 of carbonic acid. This ring is separated by a clear zone from the 

 active sperm in the rest of the suspension. " If the external edge 

 of the clear zone be carefully observed, the spermatozoa can be 

 seen to detach themselves one by one from the general suspen- 

 sion and pass straight over to the ring" (Lillie, F. R., 1913, p. 535). 



It is apparent that increase in the hydrogen ion or in the 

 carbon dioxide concentration or decrease in the oxygen con- 

 centration 1 decreases the activity of spermatozoa, while de- 



1 The observations of Drzewina, A., and Bohn, G. (Drzewina, A., and Bohn, G., 

 1912) upon the effects of lack of oxygen upon the length of life of spermatozoa will 

 be considered in another place. 



