Trill/Joined Trill
Physiology
Most Trill are distinguished by two rows of spots going down each side of their body, from forehead to toe. One of the main neurotransmitters in the Trill brain is isoboramine. Joined Trill are also extremely allergicto insect bites; the biochemical connections between the host and symbiont cannot tolerate the reaction caused by the insect's venom. One Trill peculiarity is that they are known for having cold hands.
The few Trill that are given a symbiont are typically joined in their early to mid-twenties. The physical process of being joined is irreversible. Once joined, the host and symbiont are dependent on each other after 93 hours. If the symbiont is removed from the host, symbiont and host will die within hours, even if they are otherwise healthy, unless they are reimplanted with another host or symbiont.
The Trill brain had two cerebral nuclei and two different brain wave patterns. Julian Bashir compared them with two linked computers, which both work for the same task,
Joining
On average, only 300 symbionts are available for hosting each year. Because there are many more humanoid Trill than symbionts, prospective hosts are weeded out by a demanding selection procedure, overseen by theSymbiosis Commission. The competition for the few symbionts is fierce and attracts the brightest and most highly motivated of Trill society. Often the would-be hosts excel in their chosen fields and it is not uncommon for them to hold several degrees or distinctions prior to their joining. Prospective hosts may eventually become initiates under the supervision of a field docent, a joined Trill who evaluates the prospective host's suitability for joining and makes a recommendation to the Commission. A negative recommendation usually means the initiate is cut from the joining program.
Common belief in Trill society holds that only one in 1,000 Trill make acceptable hosts. In fact, this figure is vastly understated, and nearly half of the Trill population is capable of being joined. The myth is perpetuated very carefully, though, in order to avoid the widespread chaos which would arise if the information were made public, since the symbionts would become, essentially, objects to be fought over, as people fought to gain the few prized symbionts.
Unless the joined Trill objects, a prospective host may request a specific symbiont. If a host is weak, the personality of the symbiont will overwhelm it. The joined Trill has several tools at their disposal for dealing with various aspects of their previous hosts. The telepathic ceremony of zhian'tara allows a current host to divest the symbiont of the personality and all the memories of a previous host, which are temporarily hosted in volunteers. The transferring process is performed and supervised by a symbiont Guardian, an unjoined Trill telepath. The ceremony creates a chance for closure by having the new host address the previous hosts directly as a means of distinguishing their voices and cementing the sense of finality of its latest transition. Similarly, the Rite of Emergence can focus the voice of a single previous host among the memories of the other, allowing for a more direct converse in times of need for the current host.
