EFFECT OF FOREIGN BLOOD AND CELL EXTRACTS 197 



Arbacia. 1 It was found that if the eggs were sensitized against 

 ox serum they are sensitized against other foreign blood and 

 tissue extracts. 



The question is : How does SrCl 2 (or BaCl 2 ) cause these sensi- 

 tizing effects? This is possibly answered by the observation 

 that if the unfertilized eggs of purpuratus remain permanently 

 in the SrCl 2 solution, they will ultimately form membranes 

 without requiring any further treatment. The time required 

 for this effect differs for the eggs of different females. If eggs 

 which have formed a membrane upon treatment with SrCl 2 

 (or BaCl 2 ) are subsequently exposed to a hypertonic solution 

 they will develop into larvae. The fact that the SrCl 2 alone 

 can cause membrane formation if the eggs are exposed to it 

 for a sufficiently long time suggests that the sensitivation con- 

 sists in a modification of the cortical layer of the egg of a char- 

 acter similar to that which leads to membrane formation. SrCl 2 

 thus facilitates the subsequent membrane formation by serum. 



The following facts are of interest. I had already noticed 

 in my experiments on heterogeneous hybridization that the eggs 

 of the sea-urchin can be fertilized in larger numbers with the 

 sperm of Asterias than with the sperm of Pycnopodia or Asterina. 

 It was found that the extracts of the coecum of these three 

 species of starfish showed the same relative difference in their 

 power of causing membrane formations in the unfertilized 

 egg of S. purpuratus that had previously been sensitized with 

 SrCl 2 . This agrees with the fact, which we shall prove in the 

 next chapter, that the membrane formation by the spermato- 

 zoon is caused also by a cytolytic agent a lysin; and that the 

 lysins contained in the coecum show the same relative efficiency 

 as the lysins contained in the spermatozoa of the three species. 

 It may be of interest that the extracts of all kinds of starfish 

 cells, even of the eggs, were able to bring about the membrane 

 formation in the sea-urchin egg. 



1 Loeb and Wasteneys, Science, XXXVI, 255, 1912. 



