By varying the duration of the exposure to the salt water or the amount of salt added, a point can be reached where some, but not all, of the amoebae are destroyed.
Whether few or many survive depends upon the degree of injury produced.

Much the same phenomena can be produced by gradually heating the water in which the amoebae are contained.

It is even possible gradually to accustom such small organisms to an environment which would destroy them if suddenly subjected to it, but in the process of adaptation many individuals will have perished.
It is evident from such an experiment that when a living organism is subject to an environment to which it has not become adapted and which is unfavorable, such alterations in its structure may be produced that it is incapable of living even when it is again returned to the conditions natural to it.

Such alterations of structure or injuries are called the _lesions_ of disease.

We have seen that in certain individuals the injury was sufficient to inhibit for a time only the usual manifestations of life; these returned when the organism was removed from the unfavorable conditions, and with this or preceding it the organisms, if visibly altered, regained the usual form and structure.