1895.] Vegetable Physiology. 935 
is a clear zone often 7 mm. broad, sharply marked on the inside, 
then an intensified zone gradually shading off on the outside. With 
the typhoid bacillus the clear zone is much broader, often 1 cm. across, 
but the peculiarity is the character of the intensified zone. This is 
about 2 mm. across, more intense on the outside, away from the 
metal, and in different cases more or less double, i. e., there is a narrow 
almost clear zone running all around which divides the intensified zone 
into two zones. Charcoal.—No reaction. Silicon—Do. Aluminum. 
—Do. Mobium—Do. Antimony.—With Staphylococcus p. a. this 
metal gives a clear sharp zone about 1 cm. wide, then a zone about 5 
mm. wide where there is diminished growth. In one of the plates there 
was only a very narrow clear zone. With the colon bacillus there is 
a breadth of 8 mm. where the growth of the colonies is somewhat thin- 
ner than on the rest of the plate, but no clear zone. The intensified 
zone is quite distinct and about 1 mm. broad. With the typhoid 
bacillus there is an almost clear zone of 1 cm., then an intensified zone 
2mm. broad. With the anthrax bacillus there is a perfectly clear 
zone 1.8 cm., then an indistinct intensified zone. With the cholera 
bacillus there is no sharply marked clear zone, but diminished growth 
can be made out as far as 1.5 cm. to 2 cm. around the metal. Bis- 
muth.—Staphylococeus p. a. with this metal gives a clear zone about 2 
mm. wide and an indistinct, narrow, intensified zone. With anthrax 
cultures there isa clear zone 1 mm. wide. Pyocyaneus, cholera, ty- 
phoid and colon bacilli gave no reaction with bismuth. Jron.—A 
bright polished wire nail gave a clear zone about 7 to 10 mm. wide 
with the typhoid bacillus and with the colon bacillus. Other organ- 
isms were not tested. Behring is said to have obtained negative re- 
sults with iron. Nickel—Pure nickel failed to give any reaction with 
most of the micro-organisms tested. Platinum.—Platinum wire and 
platinum black failed to give any reaction with any of the micro-or- 
ganisms tested. From the above results it is notable that it is precisely 
those metals that are resistent toward chemical reagents in general 
which fail to show any reaction or do so only to a limited extent. On 
the other hand, metals that are readily attacked by chemical reagents 
all exhibit a marked inhibitory action on the growth of the bacteria. 
The effect is, therefore, probably due to a solution of the metal in the 
medium, and putting bits of metal on the cultures is really equivalent 
to the addition of a small amount of that salt of the metal formed by 
the action of the nutrient medium. Traces of the metal may, more- 
over, be detected by chemical reagents in the nutrient medium sur- 
rounding the metal. The explantion of the clear zones is thus quite 
