3850 Hoyt: CULTURES OF SPIROGYRA 
tioned, that the internal conditions or the physiological state of 
organisms used in experimentation of this sort must always be 
taken into account. 
In this portion of the work, no evidence was obtained for a 
specific action of the calcium salts in antagonizing other salts. 
The action of CaCl, in antagonizing MgSO; and KCl was no more 
pronounced than was that of KCI in counteracting the toxicity 
of MgSO, and of CaCh, and that of MgSO, in counteracting the 
toxicity of KCl and of CaCl. These results seem strongly to 
support the conception of Loeb (14) and Osterhout (22, 25) of 
the importance of physiologically balanced solutions. MgSO, 
CaCl, and KCl, when used separately, and a mixture of three 
potassium salts were all extremely toxic in the present investiga- 
tion, but when the salts of any two of these bases were brought 
together (as in combinations of MgSO, and CaCk, MgSO, and 
KCL, KCl and CaCl) the resulting solution was much less toxic. 
A mixture of the three potassium salts here employed was as toxic 
as KCl alone and only when salts of all three metals were present 
in favorable proportions was good growth obtained. Results 
similar to these were reported by Bokorny (2). As it has been 
shown by several workers that Spirogyra requires calcium, these 
facts cannot be interpreted by supposing that this alga differs 
from higher plants in being able to survive in the absence of this 
element. 
The improvement produced in the weaker toxic salt solutions 
by animal charcoal may be considered as probably due to the 
adsorptive action of the finely divided carbon. The beneficial 
effect of the addition of colloidal platinum to toxic solutions may 
have been likewise due to its adsorption of the toxic salts. 
The author is gratefully indebted to Prof. B. E. Livingston 
for helpful suggestions in the preparation of this paper. 
SUMMARY 
1. Cultures of Spirogyra longata (Vauch.) Kg. were kept under 
laboratory conditions in a vigorous state during the entire period 
of the experiments,—more than 60 days. Crone’s solution was the 
best of the nutrient solutions tested, and that of Molisch was 
almost as satisfactory, but the solution of Sachs seemed slightly 
