60 Journal of the Mitchell Society. [ June 
any given soil. But when any one of these four is wanting 
dire results follow. 
The results that may be obtained, even where all these 
elements are present in proper proportion, depend upon the 
size of the soil particles, upon the number of grains of soil in 
the little measure of a gram; for the freedom with which the 
film of soil moisture moves over the soil grains determines 
the amount of plant food taken out of the soil. If the farmer 
is a raiser of truck for the early market, the soil for his 
lettuce, peas, beans, onions and radishes must be of a certain 
well-defined structure — it must have at least one billion, 
nine hundred and fifty millions of particles in a gram, in less 
than a thimbleful of earth. If he is going in for ordinary 
summer and autumn vegetables, corn and cabbage and potatoes, 
then there must fie at least two billion additional particles in 
each g'ram of soil. If he is a wheat planter he must be sure 
that there are not less than ten billion, two hundred millions 
of particles in his little thimbleful of soil; while for wheat 
and grass land combined the soil must be in finer particles 
still. 
While it has been known for at least two centuries that 
bacteria exist in the soil, it is only recently that they have been 
studied with any degree of satisfaction. They exist every- 
where in earth and air and sea. They were believed at one I 
time to have animal life, but they are now almost universally 
accepted as low forms of vegetable life. Over a thousand 
different kinds are now known, and the list is being steadily 
added to as knowledge of them increases. They increase by 
dividing themselves in two, and this they do at a marvelous 
rate of progression. One of them, according to a bacteriolo- i 
gist who has studied it closely, would, if left to itself, 
produce seventeen million descendants in twenty-four hours, i 
Another scientist calculates that another particularly rapid « 
multiplier could produce, if it had penty of food, four j 
thousand seven hundred and seventy-two billion progeny in a 
single day. They differ from plants which we see growing t 
