SRD:Poison

Poison (Ex)
Poison attacks deal initial damage, such as ability damage or some other effect, to the opponent on a failed Fortitude save. Unless otherwise noted, another saving throw is required 1 minute later (regardless of the first save’s result) to avoid secondary damage. A creature’s descriptive text provides the details.

A creature with a poison attack is immune to its own poison and the poison of others of its kind.

The Fortitude save DC against a poison attack is equal to 10 + 1/2 poisoning creature’s racial HD + poisoning creature’s Con modifier (the exact DC is given in the creature’s descriptive text).

A successful save avoids (negates) the damage.

See also: poisons.