BACTERIA IN THE SOIL. 643 
and down. But for the purpose of obtaining pure cultures from sin- 
gle colonies of the various species present, we should prefer to wash 
the earth in distilled water and to allow the sediment to settle before 
taking a portion of the water to add to the nutrient medium. 
In some experiments made in 1881 Koch ascertained that in soil 
which had not been disturbed but few bacteria were to be found at 
the depth of a metre; and this fact has since been established by the 
extended researches of Frankel, who devised a special boring instru- 
ment for obtaining samples of earth from different depths. Miquel, 
in 1879, estimated the number of bacteria in one gramme of earth 
collected in the park of Montsouri, Paris, ata depth of twenty centi- 
metres, at 700,000; and in a cultivated field which had been treated 
with manure,.at 900,000. The following results were obtained by 
Adametz: One gramme of earth from a sandy soil contained at the 
surface 880,000, at a depth of twenty to twenty-five centimetres 
400,000 ; the same quantity of clayey soil contained at the surface 
500,000, at a depth of twenty to twenty-five centimetres 460,000. 
In experiments made by Beumer (1886) and by Maggiora (1887) 
considerably greater numbers were found, but the last-named ob- 
server, in some instances at least, kept the earth for some time after 
collecting it, which may have materially influenced the result. 
Beumer obtained from a specimen of sandy humus taken from a 
depth of three metres 45,000,000 to the gramme; at four metres, 
10,000,000; at five metres, 8.000,000; at six metres, 5,000,000. 
These specimens were obtained from the vicinity of hospitals at 
Greifswald. In a churchyard, at a depth of four metres, the num- 
ber in one experiment was 1,152,000, and in another 1,278,000. 
Frankel has given special attention to the examination of undis- 
turbed soil not in the immediate vicinity of dwellings. In samples 
from a fruit orchard near Potsdam he found that the superficial 
layers contained from 50,000 to 350,000 germs per cubic centimetre. 
The greatest number was not immediatel; upon the surface, but at 
from one-quarter to one-half metre below the surface. The num- 
ber was found to be greater in summer than in winter, the maximum 
being in July and August. Ata depth of three-quarters of a metre 
to a metre and a half there wasavery great and abrupt diminutionin 
thenumber of germs, From 200,000 at one-half metre the number fell 
to 2,000 at a depth of a metre, from 250,000 at three-quarters of a 
metre to 200 at one metre, etc., and at a depth of one and one-half 
metres, in some instances, no more living germs were obtained. In 
other experiments a few colonies developed from earth obtained ata 
depth of three or four metres, but these were slow in making their 
appearance, and often several days, or even weeks, elapsed before 
they became visible in Esmarch roll tubes. In experiments with sur- 
