126 JACQUES LOEB 



We shall have to return to these data in a later chapter when we 

 discusp the relation between cluster formation and fertilization. 



The following experiments were carried on with the sperm of 

 S. purpuratus and the supernatant sea water of the eggs of the 

 same species, unless the contrary is stated. 



APPARENT SURFACE TENSION PHENOMENA AND CLUSTER 



FORMATION 



In analyzing the formation of these clusters the writer was 

 struck with the fact that the cluster formation showed peculiari- 

 ties which resembled the action of surface tension. The clusters 

 were usually spherical, or had a tendency to become so. When 

 two clusters were brought into contact with each other they fused 

 at once into one spherical cluster with a larger radius, a behavior 

 which would also be observed in the case of drops of substances 

 immiscible with water under similar conditions. The formation 

 of the clusters themselves resembled surface tension phenomena. 

 When a drop of purpuratus sperm is gently agitated in a little 

 dish with a few cubic centimeters of ordinary sea water streaks 

 and cylindrical masses of sperm are formed in the water which, 

 however, show nothing that reminds one of surface tension 

 phenomena. The spermatozoa are gradually scattered without 

 surface tension offering any resistance to the scattering. 



If the same experiment is made in the supernatant sea water 

 from the eggs — in egg-sea water — the streaks of Sperm produced 

 by agitation behave somewhat like oylinders of a very viscous 

 substance which is immiscible with water, e.g., a viscous oil or a 

 calcium soap. Short streaks or cylinders contract into spherical 

 masses, the above described clusters; and long cylinders break 

 up into a series of small clusters. 



In an attempt to account for this apparent or real role of surface 

 tension in cluster formation the writer thought first of the possi- 

 bility that it might be due to an agglutination of the masses of 

 sperm under the influence of the egg-sea w^ater. A study of the 

 real phenomenon of sperm agglutination, however, showed that 

 it does not lead to any formation of spherical clusters. The 

 writer had shown eleven years ago that real sperm agglutination 



