644 BACTERIA IN THE SOIL. 
face soil, on the contrary, a multitude of colonies developed within 
twenty-four to forty-eight hours, and, as many liquefying bacteria 
were present, it was necessary to make the enumeration on the first 
or second day, at which time, no doubt, many of the bacteria present 
had not yet formed visible colonies. The results obtained have, 
therefore, only a relative value. 
The most important fact developed by Frankel’s researches is that 
in virgin soil there is a dividing line at a depth of from three-quarters 
to one and one-half metres, below which very few bacteria are found, 
and that, consequently, the ‘‘ ground-water region ” is free from micro- 
érganisms, or nearly so, notwithstanding the immense numbers pre- 
sent in the superficial layers. 
The extended researches of Maggiora, made in the vicinity of 
Turin, led him to the following conclusions : 
1. The number of germs in desert and forest soils is much smaller, other 
conditions being equal, than in cultivated lands, and in these it is less than 
in inhabited localities. 
2. In desert soils the number of germs bears a relation (a) to the geologi- 
cal epoch to which the lands belong, and, within certain limits, to the height 
above the level of the sea—the older the soil and the greater the altitude, 
other things being equal, the fewer the germs ; (6) to the compactness and 
aération of the soil—the more compact and impermeable to air the smaller 
the number of germs capable of developing in gelatin ; (c) to the nature of 
ie soil—sandy soils contain fewer germs than soils rich in clay and in 
umus. 
3. In cultivated lands the number of germs augments with the activity 
of cultivation and the strength of the fertilizers used. 
4, In inhabited localities the number of germs in the superficial layers is 
very great. In the deep layers it usually diminishes rapidly, as is the case 
in all other soils. 
As to the kinds of bacteria present, and their biological characters 
and functions in preparing organic material for assimilation by the 
plants whose roots penetrate the soil, we have yet much to learn. 
Frankel remarks that the species most frequently encountered in the 
deeper strata of the soil were three bacilli which also abound in the 
superficial layers—viz., the ‘‘ hay bacillus,” the ‘‘ wurzel bacillus,” 
and the “‘hirnbacillus.” In all eleven bacilli were isolated and cul- 
tivated. Micrococci were only found four times, and spirilla not at 
all. Mould fungi were more abundant, and especially one previously 
obtained from the air by Hesse and called by him “‘ brauner Schim- 
melpilz.” Anaérobic bacilli, contrary to expectation, were not ob- 
tained in Frankel’s researches, and no pathogenic species were found 
in the deeper layers of the soil. We have already referred to the 
fact that the bacillus of malignant cedema and the bacillus of tetanus, 
two pathogenic, anaérobic species, are common in rich surface soil in 
various parts of the world. 
