1922] GREAVES—SOIL 167 
produced was 50 per cent of normal, the osmotic pressure was 9.5 
atmospheres. Table VI gives these data for both ammonification 
and nitrification. 
The nitrifiers, therefore, are more sensitive to osmotic changes 
than are the ammonifying organisms, but in both cases the toxicity 
increases more rapidly than does the osmotic pressure. This is 
very rapid in the case of the nitrifiers. 
TABLE V 
OSMOTIC PRESSURE OF SALT-TREATED SOIL TOXIC TO NITRIFYING ORGANISMS 
Chloride Nitrate Sulphate Carbonate Average 
ge EEE ee tet ed 1.81 1.80 1.84 1.82 
POM ii. a5 ee: 563 1.67 1.75 1.49 1.61 
Calcium bt ee oe 1.60 HE? tae been aera 1.54 1.56 
Magnesium............ 1.81 1.59 1.88 1.79 1.78 
BARDBOROOE. oii ae ccs 1.65 2:93" a.30 2.01 1.96 
PoC ET Se ae: 4.94* 1.89 1.85 1.86 1.87 
PVETEGO 6 oss, 1.65 1.70 1.90 ey ges RG eee 
* Not counted in the average. 
TABLE VI 
OSMOTIC PRESSURE TO REDUCE 
ON OF PRODUCT 
Ammonification Nitrification 
I per cen I per cent 
10. Det Cent oa Go ©.255 atmospheres | 0.197 atmospheres 
a5 per Cent ste eg ©.199 atmospheres | 0.117 atmospheres 
SO Per Cont icc ©.190 atmospheres | 0.088 atmospheres 
The average for the anions in the case of the nitrifiers is within 
experimental error, the same as that for the ammonifiers. The 
average for the cation is slightly lower for the nitrifiers than for the 
ammonifiers, but quite similar in both series, thus indicating that 
the toxicity in both sets is governed by the same factor, possible 
Osmotic pressure plus a physiological effect produced by the salt. 
The physiological influence may be due to the replacing of ion in 
the living protoplasm, thus changing its physical, chemical, and 
electrical properties so that they are incompatible with life. It is 
thus assumed with Logs (18) that the toxicity of sodium salts on 
entering the cell is due to the formation of sodium proteinates, 
