EFFECT OF FOREIGN BLoopD 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 
UD COUtE Ee of | Percentage of 
eggs at r Eggs That 
Temperature Harnied | Temperature Rocnicd 
Membranes | Membranes 
1" Che eee 3 Wtes Deeg cosas, ante eons 100 
Lon Ge 3 oar Sie ae te a 100 
30) Oi, es ene 5 S502 © sires Scene a: 1 
SO PN Sac. cd ays 70 i npebidinloatans oe atee ete 0 
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, 
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 XX XVII 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,. Somewhat better results were obtained if 
about six drops of sea-water were added to the mixture of serum 
and SrCl,. The addition of BaCl, had a similar effect to that 
of SrCl,. But it is troublesome to work with BaCl, on account 
