App. H— Glossary of Acronyms and Terms • 429 
of intermediate duration, with exposure to a test sub- 
stance for 3 to 6 months. 
Testing: Standardized procedures that have been dem- 
onstrated to predict certain health effects in humans 
and animals. Testing involves the frequent repeti- 
tion of well-defined procedures with measurement 
of standardized biological endpoints. A given test may 
be used to test many different substances and may 
use many animals. Testing is used to establish the 
efficacy, safety, and toxicity of substances and pro- 
cedures. 
Tissue Culture: The maintenance in vitro of isolated 
pieces of a living organism. The various cell types 
are still arranged as they were in the original organ- 
ism and their differential functions are intact. 
Toxic Substances Control Act (TSCA): This act au- 
thorizes EPA to regulate substances that present an 
unreasonable risk of injury to health or to the envi- 
ronment. The act also requires the reporting or de- 
velopment of data to assess the risks posed by a given 
substance. 
Toxicity Testing: The testing of substances for toxic- 
ity in order to establish conditions for their safe use. 
There are now more than 50,000 chemicals on the 
market and 500 to 1,000 new ones are introduced 
each year. The Federal agencies with the largest role 
in toxicity testing are FDA, EPA, CPSC, and OSHA. 
Toxicology Data Bank (TDB): Made public by the 
NLM in 1978, the TDB provides toxicity information 
on more than 4,000 chemicals and substances. TDB 
information is based on conventional published 
sources. 
Tranquilizer: An agent that quiets, calms, and reduces 
anxiety and tension, with some alteration of the level 
of consciousness. 
T-test: An estimate of the difference between the mean 
values of one parameter of two treatments . This can 
be a powerful measure when the number of compari- 
sons is small, but the potential for error increases 
as the number of parameters grows. 
Veterinary Medicine: The maintenance and improve- 
ment of the health and well-being of animals, par- 
ticularly the 30 to 40 different species of animals of 
economic, ecological, and environmental importance. 
Veterinary medicine is closely allied with veterinary 
research. 
Veterinary Research: A branch of biomedical re- 
search devoted to the understanding of the life proc- 
esses of animals and the application of this knowl- 
edge to serve animals as well as humans. 
