FERTILISATION 213 



While suggesting that restrictions to the power of cross-fertilisation 

 may be due to difterfences in surface tension, Loeb admits that the 

 evidence seems to show that the capacity to conjugate is to some 

 extent at least specific. Attempts were made to fertilise the eggs of 

 sea-urchins with the spermatozoa of Annelids and Molluscs, but 

 these experiments were without success. Kupelweiser,^ however, 

 reports that he has been successful in fertilising Strongylocentrotus 

 ova with the spermatozoa of the mussel (Mytilus), and that the 

 products developed into gastrulse. 



Gray^ finds that the spermatozoa of Hchinus miliaris in sea- 

 ^water are affected by positive trivalent ions such as those of Ce and 

 La, in much the same way as colloidal particles of albumen and 

 globulin. It is only those solutions that are capable of maintaining 

 the normal negative charge, on the sperm unaltered that allow 

 vigorous movement of the sperm. Trivalent positive ions flocculate 

 sperm suspensions by lowering this negative charge.^ ' The action of 

 H' is very intense and changes the surface charge on the sperm from 

 negative to positive without any intermediate flocculation. The work 

 of Teague and Buxton^ shows that living cells (bacteria) are much 

 more sensitive to flocculation than dead cells or mastic particles. 

 Girard and Audubert* claim' 'that bacteria owe most of their 

 biological properties, such as viability, pathogenetic power, etc., to 

 their surface charge.^ In the same way Gray suggests that the action 

 of H"-ion in bringing about the varioixs effects found in heterogenous 

 hybridisation experiments- is to be explained by the action of this ion 

 on the membrane charge of eggs and sperm. If sperm are placed in 

 sea-water to which a certain amount of acid is added, their surface 

 charge is reduced considerably below normal. Eggs put in the same 

 solution will have their charge altered to a different degree, and thus 

 the results of heterogenous hybridisation could be explained in a 

 simple manner. 



Dr. A. T. Masterman tells me that, in certain cases, hybridisation 

 among fishes may be induced more readily in -the absence of 

 opportunity for normal fertilisation, that is to say, for fertilisation 



1 Kupelweiser, " Versuche iiber Entwiokelungseri'egung und Membran- 

 bildung bei Seeigeleiern durcli MoUusksperma," Biol. Centralbl.,- vol xxvi., 

 1906. 



2 Gray (J.), "The Eelation of Spermatozoa to Certain Electrolytes," II., 

 , Proa. Roy. Soc. Zand., Ser. B., vol. xci., 1920. 



^ Teague and Buxton, "Die Agglutination in Physikalischen Hinsiolit," III., 

 Zeitsoh.f. Physikal. Ckem., vol. Ivii., 1906. 



* Girard and Audubert, " Les charges 61ectrique des microbes et leur tension 

 superficielle," Compt. Rend. Acad. Science., vol. clxvii., 1918. 



* In the case of an asporogonous strain of Anthrax, the reduction of the 

 normal charge of the double electric layer (cd) from a value of 3-68 to 2'47 x 10"'' 

 C.G.S., quintuples the normal growth of the culture, while by the reduction of 

 the value of o-d to 0, many pathogenetic bacteria are rendered harmless. 



