POLYSPERMY II7 



over wide limits, quite apart from differences in threshold suscepti- 

 bility between different egg batches. The question as to which of 

 these two, a or the block, is influenced by nicotine can be examined 

 by the method of known sperm-egg interaction times. The pro- 

 cedure is shown diagrammatically in Fig. 25. Such experiments 

 show (Rothschild, 1953) that nicotine abolishes or slows up the 

 fast partial block to polyspermy. According to the concentration 

 of nicotine used and the duration of its application to the un- 

 fertilized egg, the conduction time of the nicotine-modified block 

 to polyspermy can be extended to an almost indefinite extent. 



2,25 



4,25 



FIG. 25. — Experimental procedure for investigating effect of nicotine on the 

 block to polyspermy. The curved lines with arrows show which vessels 

 are emptied into which. The numbers by the curved lines refer to the times 

 of emptying, e.g. 2, 25 means that vessel c was emptied into vessel d 2 min. 

 25 sec. after the beginning of the experiment, which started when b was 

 emptied into c at t — o, a, 10 ml. of sperm suspension; b, 2 ml. nicotine in 

 sea water (i/iooo, v/v); c, 2 ml. egg suspension; d, 90 ml. hypotonic sea 

 water (28 %) ; e, 700 ml. sea water + 2 1 ml. 11% NaCl in sea water (Roths- 

 child, 1953). 



Hagstrom & Allen (1956) have recently tried to re-examine the 

 problem of nicotine-induced polyspermy in sea-urchin eggs, using 

 the method of known sperm-egg interaction times. They con- 

 clude, on rather slender evidence, that the 20-second cortical 

 change, described by Rothschild & Swann in 1949, is the block to 

 polyspermy. Attractive as this idea may be, there is a considerable 

 body of evidence which makes it unacceptable, quite apart from 

 experiments with nicotine. Hagstrom & Allen have failed to 

 appreciate the importance of this evidence. For example, in 

 attempting to explain the fact that even when eggs are heavily in- 

 seminated, the proportion of polyspermic eggs is very low, they 

 postulate that the acid produced by sea-urchin eggs at fertilization 

 kills or inactivates supernumerary spermatozoa before they can 



