590 STUDIES IN GENERAL PHYSIOLOGY 
loids has to be maintained. This requires certain ions in 
definite proportions, either Na, K, and Ca (or other combi- 
nations, for instance Mg and Ca). Distilled water is a poison 
for the eggs of Arbacia. Hence, if Na be one of the ions of 
the surrounding solution, Ca and K ions are likewise required. 
My results differ somewhat from those obtained by 
Herbst.’ But I pointed out in my last paper that Herbst 
was misled by his method.’ This method consisted in 
making a solution of the same complication as the sea- 
water, in which, however, one constituent was omitted. In 
case the eggs did not develop in such a solution, this was 
considered a proof that the constituent omitted was neces- 
sary for the development of the eggs. My experiments 
show that this conclusion is not correct. It is quite possible 
that the substance which was omitted or removed was not 
directly necessary for the egg, but only indirectly, inasmuch 
as it served to counteract the poisonous effects of another 
constituent of the solution. 
It seems to me that my experiments necessitate the intro- 
duction of a new conception, namely, that of physiologically 
balanced salt solutions. By this I mean salt solutions which 
contain such ions and in such proportions as completely to 
annihilate the poisonous effects which each constituent would 
have if it were alone in solution. Sea-water and blood (and 
approximately a mixture of 96 c.c. 4n NaCl+2 c.c. Yn 
CaCl, +2 e.c. $n KCl) are physiologically balanced salt 
solutions. 
It will be necessary to investigate how far the conclusions 
of pharmacologists, botanists, and bacteriologists concerning 
the effects of various salts require a correction on the basis 
of these new facts and conceptions. Their consideration 
might even prove of use in problems of immunity and 
adaptation. 
1 Hersst, loc. cit., Vol. V (1897), p. 649. 2Part II, p. 559. 
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