STUDIES OF FERTILIZATION 555 



another egg-extract. This time the agglutination was complete for it 

 could not be repeated a third time. Other sperm suspensions gave 

 similar results. 



The result might be interpreted as a purely biological reaction, 

 that is to say in terms of stimulation, were it not for the fact that 

 the agglutinating substance disappears from an agglutinated 

 sperm suspension, as shown by the following experiment: 



September 12, 1912. Arhacia. Nine parts of a thick active sperm 

 suspension was agglutinated by one part egg-extract. The agglutina- 

 tion produced was so strong that the fluid between the white masses 

 appeared clear to the eye. In three or four minutes reversal of the agglu- 

 tinations had begun. The agglutinated sperm suspension was then 

 centrifuged until practically all the sperm was precipitated. The super- 

 natant fluid was tested and agglutinin was shown to be absent. As 

 control, a dilution of one part of the same egg-extract with 9 parts of 

 sea-water was tested with the same sperm and proved to be strongly 

 agglutinative. Three tests were made with each with uniform results. 



There can be no doubt, as the result of this and other observa- 

 tions also, that the spermatozoa fix in some way the agglutinating 

 substance, and it will be simplest to assume as a working hypothesis 

 that the fixation is due to chemical union. I have not yet had the 

 opportunity to ascertain if the agglutinin could be regained from 

 the sperm precipitated in the centrifuge. 



5. Nature of the effect on the sperm 



We have noted four effects of the egg-extracts on sperm of the 

 same species, namely: (1) Stimulation of intense activity, which is 

 of brief duration. This is more marked in the case of the sperm of 

 Arbacia, than in the case of the naturally extremely active sperm 

 of Nereis ; (2) An orienting effect expressed in positive chemotaxis ; 

 (3) An agglutinating action; (4) Following these effects more or 

 less complete paralysis of the sperm. 



To what kind of change in the individual spermatozoa is the 

 agglutination reaction due? We may note in the first place that 

 the agglutination is between the heads of the spermatozoa, and 

 that the tails are apparently unaffected, at least at first; it is only 

 in later stages of the action of the agglutinating substance that 

 the locomotor function is injured. The adhesion of the heads 



