Biting and sucking insects have been found to carry the bacilli from one plant to another.
The lactic acid bacilli are given either in the form of tablets or milk soured by them, or cheese made from the sour milk.
By growing this bacillus in broth a toxin is formed which remains in solution and can be separated from the bacilli themselves by filtration.
In the same way sterilized cultures of typhoid bacilli have been used to protect against attacks of typhoid fever, and an anti-typhoid serum has been employed with intent to cure.
To these injurious microbes Metchnikoff has given the name of "wild," and he proposes to restore health by giving "tame" microbes, such as lactic acid bacilli.
