Shigella dysenteriae (type Shiga) has been cultured in chick embryo using Tanaka's method in which a hen's egg is settled in a longitudinal, standing position, that is, with its dull point up and its sharp one down.
After several chick embryo passage uses the virulence of Shigella dysenteriae increased in the chick embryo, and then it increased in mice.
It has been demonstrated that after several passage uses in certain species of animals, virulence increased in other species of animals as well as the passage animal.
The above-mentioned fact explains the mechanism of some epidemic infections.
