1922] GREAVES—SOIL 165 
Possibly potassium carbonate is more toxic to the nitrifiers of 
the soil than it is to the nitrogen-fixing organisms. It is certain 
that the azofiers in soil are much more resistant to these salts than 
are the other classes of microorganisms. The concentration of 
the salts in the soil was not high enough to permit conclusion as to 
the relative toxicity of the various anions and cations. The tests, 
however, make it certain that alkali soils which have a vigorous 
nitrifying or ammonifying microflora will maintain a vigorous 
azofying flora, even though they contain considerable quantities 
of soluble salts. 
The influence of an anion upon the internal friction of colloids 
varies with concentration and reaction of medium, and it is interest- 
ing to note that the series for the ammonifiers is the same as that 
for acid solutions of proteins, whereas that for the nitrifiers is the 
order for these ions upon a neutral or alkaline solution of the 
protein. If, therefore, toxicity of these salts is due in a measure to 
their changing the internal viscosity of the protoplasm, we should 
have to assume a slight difference in the protoplasm making up 
the cell of the two groups of microorganisms, the one being electto- 
positive and the other electro-negative. 
The order of toxicity of the cation to the ammonifiers is not far 
different from what would be expected if toxicity were due to a 
precipitation of the protoplasmic:-colloids. When the nitrifying 
series are examined in the light of the HOFMEISTER series, however, 
the potassium ion is found on the opposite extreme of the series 
from where it should be. 
Whether this is due to analytical error or to the potassium ion 
being especially poisonous because of its changing the state of 
turgescence of the organic colloid is not clear. It would appear, 
however, that if the latter were the correct explanation, we might 
expect potassium to change positions in the ammonifying series. 
This would appear more reasonable, for both the ammonifiers and 
nitrifiers function normally in the same medium, and the same 
evolutionary forces have been at work bringing these organisms to 
their present condition. 
The relative toxicity of the anions toward ammonifiers and the 
relative toxicity of the cation as measured in terms of both ammoni- 
