362 BOTANICAL GAZETTE [NOVEMBER 
jars in every case were provided with cotton plugs and the whole 
outfit was sterilized before using. In these experiments pure cultures 
were used, and the medium, in this case water, was also sterilized 
before being inoculated. In one series (table II) the jar was inocu- 
lated with Pseudomonas radicicola (Beyerinck) Moore, from alfalfa; 
while in the experiments shown in table III the jar was inoculated 
with Bacillus megaterium DeBary, 1°° of a liquid culture medium 
being used to inoculate the jarsineachcase. Special care was taken to 
inoculate the normal and treated jars with the same number of organ- 
isms. An examination of the tables II and III will show that there 
was a marked increase in the number of bacteria during the first 
few days asa result of electrical stimulation. The maximum in one 
case was 52,000 for the normal and 5,000,000 for the treated; in 
another case 32,000 for the normal and 7,000,000 for the treated. It 
will be noted that the subsequent decrease in the number of the 
organisms was very marked in the electrically stimulated cultures, a 
feature due to the accumulation of zinc oxid in the jar, which is 
always present as a white precipitate in galvanic cells of this type- 
The presence of zinc oxid in water formed by the action of even com- 
paratively weak currents is toxic to bacteria, and the same toxic 
effect is well illustrated in galvanotropic experiments with roots. 
Some of our experiments which were made in much smaller jars failed 
entirely, as the smaller volume of water employed became concentrated 
so quickly with this substance that a toxic effect on the organism 
occurred very shortly after inoculation. Some of the precipitate 
obtained was dried and dissolved in flasks containing sterilized water. 
The jars were then inoculated with Bacillus megaterium DeBary, 
with the result that very little increase in the number of bacteria 
occurred where a 2 per cent. solution of this prepared precipitate of 
zinc oxid was used, and a 10 per cent. solution apparently killed 
all bacteria. In both of the experiments enumerated there occurred 
a slight falling-off in the number of organisms in the normal or 
untreated cultures. This is of common occurrence, however, in 
standing water, or even in soils under certain conditions. 
The strength of current developed in these experiments (0-1 and 
o.3 milliampere) was very constant, and from the results obtained it 
is evident that it acted as a marked stimulus. A large series of 
