EFFECT OF FOREIGN BLOOD AND CELL EXTRACTS 195 



It will be seen that when the eggs are warmed to 31 C. 

 a sudden increase in the number of membrane formations 

 occurs. At 36 this effect lapses again owing to the modifica- 

 tion of the process of membrane formation. For clear drops 



TABLE XXXVI 



exude from the egg, but their surfaces do not flow together so 

 as to produce a uniform fertilization membrane. Membrane 

 formation does not occur until the eggs are cooled again. 

 Merely heating the eggs to 32 C. without the addition of 

 serum does not lead to membrane formation. If the eggs of 

 S. purpuratus are heated to 31 or over, their capacity for 

 development is destroyed. 



But I discovered another method of increasing the efficacy 

 of the blood serum without reducing the capacity of the eggs 

 for development. This consists in the addition of a m/2 SrCl 2 

 solution to the serum. 



In order to demonstrate the beneficial effect of strontium, 

 one must choose eggs that show only a slight degree of sensi- 

 tiveness toward serum. Table XXXVII sums up the influence 

 of strontium upon the number of eggs which can be made to 

 develop by serum. Each experiment was carried out upon the 

 eggs of a single female. 



In all these experiments I employed a 3/8 grammolecular 

 solution of SrCl 2 . Somewhat better results were obtained if 

 about six drops of sea-water were added to the mixture of serum 

 and SrCl 2 . The addition of BaCl 2 had a similar effect to that 

 of SrCl 2 . But it is troublesome to work with BaCl 2 on account 



