Til. 
BACTERIA IN THE SOIL. 
SuRFACE soil, and especially that which is rich in organic matter, 
contains very numerous bacteria of many different species. Some of 
these are of special interest on account of their pathogenic power. 
Thus the bacillus of malignant cedema and the bacillus of tetanus 
have been shown to be widely distributed species, which have been 
obtained by investigators in various parts of the world by inoculating 
susceptible animals—guinea-pigs or mice—with a little rich surface 
soil. Other species are interesting because of their action in nitrifi- 
cation and in the destructive decomposition of organic material by 
which it is fitted for assimilation by the higher plants. Many of the 
bacteria present in the soil dre strictly anaérobic, and in attempts to 
estimate the number and kind of microérganisms present in a given 
sample this fact must be kept in view. 
The simplest method of studying the bacteria in the soil consists 
in introducing a small quantity into liquefied gelatin in test tubes, 
and, after carefully crushing it with a sterilized glass rod and thor- 
oughly mixing it with the gelatin, making roll tubes in the usual 
way. Some of these should be put up for anaérobic cultures—z.e., 
the tube should be filled with an atmosphere of hydrogen according 
to Frankel’s method. If the object in view is to estimate the num- 
ber of bacteria in a given sample of soil the difficulty is encountered 
that, however finely crushed, the little masses of earth are likely to 
contain numerous bacteria, and we cannot safely assume that each 
colony originates from a single germ. Thoroughly washing a small 
quantity of soil, by agitation, in a considerable quantity of distilled 
water, and then adding a definite quantity of the water to nutrient 
gelatin and making roll tubes or plates, as in water analysis, sug- 
gests itself as a simple method ; but Frankel has shown that it is far 
from being reliable when the object is to estimate the number of 
bacteria. He obtained more uniform and accurate results by intro- 
ducing the earth at once into liquefied gelatin and crushing it as 
thoroughly as possible with a strong platinum wire, after which as 
thorough a mixture as possible was effected by tilting the tube up 
