1922] GREAVES—SOIL 171 
but permits foreign or unbalanced constituents to enter. These 
foreign or unbalanced salts on entering the cell protoplasm interact 
with the proteins thereof, forming within the living protoplasm 
foreign proteinates, the physical, chemical, and electrical properties 
of which are different from those of the normal protoplasm. Hence 
we have the protoplasm rendered incapable of normal functioning.. 
The first effect is governed to a marked extent by the osmotic 
pressure of the medium in which the organism is functioning, and 
the second by the specific salt, acid, or base which comes in contact 
with the protoplasm. 
STIMULATING ACTION OF SALTS.—Many salts when added to a 
medium in which bacteria are functioning first stimulate, and as 
the concentration is increased the specific salt becomes toxic. The 
TABLE VII 
PERCENTAGES OF AMMONIA PRODUCED IN SOIL TO WHICH VARIOUS SALTS WERE rceuret/ 
E UNTREATED SOIL BEING TAKEN AS 100 PER CENT 
Chloride Nitrate Sulphate Carbonate 
OOM bcs veut o, 106.0 107.8 100.0 110.1 
VOMSSHIN Ge, eo 100.0 102.2 100.0 108.9 
ACH Oe ae 100.0 100.0 103.2 114.6 
pe pe amen or tga 100.7 100.0 104.5 103.5 
DEMADONE ee kc 100 116.0 123.8 Tit .? 
POG ALG bere eles as 118.6 102.9 103.9 107.9 
extent of this stimulation varies with the salt, the concentration 
of the salt, the medium in which it is used, and the specific micro- 
organism grown upon it. If the ammonia produced in unit time 
in untreated soil is taken as 100 per cent, we obtain the values 
given in table VII for the various salts. 
All except six of the salts stimulate bacterial activity. There 
is a wide variation, however, depending upon the specific salt. The 
cations arranged in a descending order would be Mn>Fe>Na> 
Ca>K>Mg. Although there is a wide variation, depending 
upon the cation and anion, it is interesting to note that it is not 
these elements which are to be recognized as plant foods, but the 
catalizers which head the list. This also appears in the case of the 
anion where the series is SO,>Cl>CO,;>NO;. The cations would 
appear to play a greater part as bacterial stimulants than do the 
