Published online by Cambridge University Press: 15 May 2009
Susceptible mice have been placed in contact with infective individuals of the same species, separated from them after a definite period, and placed in contact with a further group of normal mice. This process has then been repeated again and again, the number of groups exposed varying, in different experiments, from three to twelve. In this way the spread of infection has been limited to that occurring between any one group and the group immediately following it.
Under these circumstances infection has spread far less readily than was the cases in other experiments, in which the mice were retained as a single population, and in which infection could spread in any direction among all the individuals at risk.