706 RALPH S. LILLIE 
vast majority undergo no apparent change and when fertilized 
next day develop into normal larvae. 
The calcium-containing solutions are thus not quite indifferent 
in their action. It is probably not possible to produce a com- 
pletely indifferent or ‘physiologically balanced’ salt-solution con- 
taining a high proportion of either of the above salts, though it 
is easier to obtain well marked antitoxic action with iodide than 
with sulphocyanate." It is well known that addition of appro- 
priate quantities of calcium, magnesium, and potassium salts 
to pure solutions of sodium chloride or bromide produces a prac- 
tically indifferent medium; but the specific toxicity of many salts, 
including the above, is too great to be thus fully counteracted. 
The case of Asterias eggs, in which brief exposure to pure isotonic 
sodium chloride solutions produces membranes and _ initiates 
development, illustrates the essential nature of the conditions 
perhaps more clearly than the above; addition of calcium chloride 
greatly checks the membrane-producing and _ permeability- 
increasing action of the pure solution, and with it the cleavage- 
initiating action, but further addition of magnesium and potas- 
sium salts, as in van’t Hoff’s solution, is required to produce a 
medium which is completely indifferent. 
Treatment with potassium iodide or sodium sulphocyanate, 
followed by hypertonic sea-water as above, gives similar results. 
The following experiments will illustrate. Eggs were placed for 
five minutes in each of the following solutions: (A) 0.55 Mm 
NaCNS, (B) a mixture of 250 ce. 0.55 mM NaCNS + 25 ce. 3 CaCl?, 
(C) 0.55 m KI, (D) 250 ce. 0.55 m KI + 25 ee.3 CaCl; they were 
then returned to sea-water. In each case part of the eggs were 
allowed to remain in sea-water; the rest were exposed to hyper- 
tonic sea-water for 30 minutes and then replaced in sea-water. 
Treatment with the pure solution alone (A and C) produced 
membranes in a majority of eggs, of which a small proportion (one 
in several hundred) formed blastulae; while of the eggs treated 
also with hypertonic sea-water the majority formed larvae, many 
of which swam vigorously at the surface and were apparently 
quite normal. Exposure to the calcium-containing solutions (B 
18 Cf. my results with ciliated cells: American Journal of Physiology, 1906, 
vol. 17, pp. 104, et seq. 
