What is "stage of incubation"

Incubation \In`cu*ba"tion\, n. [L. incubatio: cf. F. incubation.]

1. A sitting on eggs for the purpose of hatching young; a brooding on, or keeping warm, (eggs) to develop the life within, by any process.
   --Ray.

2. (Med.) The development of a disease from its causes, or its period of incubation. (See below.)

3. A sleeping in a consecrated place for the purpose of dreaming oracular dreams.
   --Tylor.

4. The maintenance (of a living organism, such as microorganisms or a premature baby) in appropriate conditions, such as of temperature, humidity, or atmospheric composition, for growth.

5. The gradual development in some interior environment, until fully formed; as, the incubation time for developing a new drug may be longer than ten years from its first discovery.

   Period of incubation, or Stage of incubation (Med.), the period which elapses between exposure to the causes of an infectious disease and the attack resulting from it; the time during which an infective agent must grow in the body before producing overt symptoms of disease.