The unprotected individuals gradually increase in number, forming an inflammable material awaiting the spark or infection which produces a conflagration in the one case and an epidemic in the other.
Cerebro-spinal meningitis is another example of a disease which exists in sporadic and epidemic form.

This disease is caused by a small micrococcus, the organisms joined in pairs.

The seat of the disease is in the meninges or membranes around the brain and spinal cord.

The micrococci enter the body from the throat and nose, and either pass directly from here into the meninges, or they enter into the blood and are carried by this into the meninges.

The organisms are easily destroyed and cannot long survive the conditions outside the body, so that for infection to take place the transmission must be very direct.
Carriers who have the organisms in the throat, but who do not have the disease, are the principal agents in dissemination.