Nature of Formative Stimulation 141 



worms, namely Sipunculides , can call forth the membrane 

 formation in the sea-urchin egg even if it is diluted a hundred 

 times or more with sea-water. This effect is not produced 

 in the eggs of every female sea-urchin but of only about 20 

 per cent of the females. I think the difference is caused by 

 differences in the permeability of the eggs for lysins; and the 

 degree of permeability seems to var}^ slightly for the eggs of 

 different females. 



Instead of wasting time on an examination of the effects of 

 the blood of invertebrates^ I examined the effects of the blood 

 serum of warm-blooded animals. I succeeded in causing 

 membrane formation in the sea-urchin egg (purpuratus) with the 

 blood serum of cattle, sheep, pigs, and rabbits; and such eggs 

 behaved like the eggs which had been treated with the living 

 sperm of roosters or with butyric acid. They began to develop, 

 but they became sickly at room temperature and soon disinte- 

 grated. If, however, they were treated after the membrane 

 formation for a short time with a hypertonic solution they 

 developed at room temperature. The blood, therefore, contains 

 the lysin, but not the second substance necessary for the 

 full development. It is, therefore, necessary to substitute for 

 the action of the latter the treatment with a h\'pertonic solu- 

 tion if we wish to call forth a normal development of the egg 

 treated with serum. 



The lysin of the blood is Uke that of the spermatozoon 

 relatively resistant to heat. The blood does not lose its power 

 to call forth membrane formation by heating it for some time to 

 60° or 65° C.2 It is curious that SrCl, and Babl, increase the 

 membrane-forming power of the blood. 



Not only blood but also the extracts of the organs of foreign 



1 Since this was written the blood and the extracts of organs of a number of 

 invertebrates were used successfully to produce the membrane formation and 

 development of the egg of the sea-urchin. 



2 The substance which causes membrane formation can bo precipitated with 

 acetone (Loeb, Pflugers Archiv, CXXIV, 37, I'JOSj. 



