Texas Code of Criminal Procedure - CRIM P Art. 49.11. Chemical analysis

(a) A justice of the peace may obtain a chemical analysis of a sample taken from a body in order to determine whether death was caused, in whole or in part, by the ingestion, injection, or introduction into the body of a poison or other chemical substance. A justice may obtain a chemical analysis under this article from a chemist, toxicologist, pathologist, or other medical expert.

(b) A justice of the peace shall obtain a chemical analysis under Subsection (a) of this article if requested to do so by the physician who performed an autopsy on the body.

(c) The commissioners court shall pay a reasonable fee to a person who conducts a chemical analysis at the request of a justice of the peace.