Nature of Formative Stimulation 143 



We now understand the paradoxical fact, that by foreign 

 sperm we can cause membrane formation and development of 

 the sea-urchin egg in two different ways: namely, first by the 

 living sperm and second by the extract from the dead sperm; 

 while the sperm of the same species can only cause the eggs to 

 develop when it is alive. We now understand the fact alluded 

 to at the beginning of this chapter that my first experiments 

 to cause the development of the egg with extract of sperm did 

 not succeed, since I took it for granted that it was necessary 

 to use the extract of the sperm of the same species from which 

 the eggs were taken. The lysins in this case were not able to 

 diffuse into the egg. 



The further unraveling of the nature of the immunity of the 

 egg-cell against the dissolved lysins of the blood and the tissues 

 of the same species depends upon the explanation of the fact 

 that the lysins of a species cannot diffuse into the egg of the 

 same species. It would be of interest if the same principle 

 formed for the immunity of the egg-cell would hold also for the 

 immunity of the body-cells against the lysins in the blood of 

 their o%vn species. 



We may, therefore, say that the substance to which the 

 sperm owes its fertilizing power is a lysin and we may express 

 the suspicion that the lysins which we have thus far kno\\TL 

 only as protective agencies against bacteria play a great physio- 

 logical role in the mechanism of life phenomena. We may call 

 our theory of the developmental action of the spermatozoon 

 the lysin theory; thereby designating that the impulse for the 

 development of the egg is given by a lysin contained in the 

 spermatozoon. In artificial parthenogenesis we substitute for 

 the natural lysin a cytolytic substance. Aside from the lysin 

 action the normal development demands, as a rule (but not 

 always), a second corrective influence which in artificial par- 

 thenogenesis may be given by a hypertonic solution. 



