Aug., 1889. 
179 
president’s address. 
and thus infect with the disease the flocks which may be 
feeding on that spot. 
Certain kinds of Bacteria that are found in soil are 
believed by many observers to have a very important effect 
upon it from an agricultural point of view. This is especially 
true of some species of Micrococci ; one, Micrococcus nitrijicans , 
was so named because it was supposed to be the especial seat 
of this power, by which the ammonia, or even the free nitro¬ 
gen, in the interstices of the soil was oxidised with the 
formation of useful nitrates. Another species, M.cereus , has 
also been described as a “ very efficacious nitrifying agent.” 
But considerable doubt has been thrown upon this belief by 
two other alleged facts : (1) That the nitrifying action goes 
on in soil in which no Bacteria can be detected, and (2) that 
“pure” cultures of some of the species said to produce this 
effect exhibit no trace of the power. Others have attributed 
the chemical action to the soil itself, which is supposed to act 
like spongy platinum, and condense the gases in its interstices. 
Moreover, there seems to be equal proof that some microbes can 
denitrify, decomposing nitrates and evolving ammonia or free 
nitrogen. It may be that in both cases the action is merely 
an inorganic one, and that the Micrococci are only accidental 
accompaniments of the process ; or it may be that the very 
same organisms can nitrify or denitrify, according to circum¬ 
stances. 
Since the lower strata of the soil contain no Bacteria we 
should expect that pure uncontaminated cold spring water, 
coming from a sufficient depth, would also contain few or none. 
This may be proved by spreading a minute drop, taken directly 
from the source, on the surface of sterilised gelatine. In 
most cases no colonies will be developed. Deep well-water 
contains very few ; ten have been found in a cubic centimetre. 
Tap water shows from 57 to 1,950 per cubic centimetre ; but 
after rain the number increases. But the slightest exposure 
alters the condition of the water at once. From 50,000 to 
100,000 have been found in a litre of water from a brook, 
and as the brook descends to the sea it rapidly becomes more 
contaminated. 
Ordinary drinking water contains Micrococcus aquatilis and 
Bacillus erythrosporus in small numbers ; but if it remains 
standing, at ordinary temperatures (say 20° C.), rapid multi¬ 
plication takes place. But there is a consolation in the 
following well-proved fact, that those species which propagate 
under such circumstances belong to the harmless kinds. 
Pathogenic Bacteria cannot live in ordinary spring water, but 
only if it contains decomposing organic matter. When 
introduced they never multiply, and after a time totally 
