How did people ever find the chemical that makes pupils dilate?

Donald Mutti, a professor at the Ohio State University College of Optometry, eyes an answer to this query:

The discovery was probably accidental. Dilating drops block receptors in the muscle that constricts the iris, the colored “curtain” of the eye that controls the amount of light traveling toward the retina. This hindrance allows the muscle that dilates the iris to act unopposed, causing the pupil—which is just a hole in the center of the iris—to enlarge.

Our pupils naturally expand in darkness and shrink in bright light through the actions of the two opposing iris muscles, the iris dilator and the iris sphincter. The dilator muscle, which extends radially through the iris, contracts to pull the iris outward, bunching it up like an open curtain. The iris sphincter is arranged in a circular pattern, similar to a purse string. Its constriction pulls the iris inward and flattens it, like a curtain drawn closed.

These muscles are under the control of the autonomic nervous system, which deals with involuntary reflex actions. Sympathetic output, which is associated with arousal, stimulates the iris dilator muscle to constrict, opening our pupils during a fight-or-flight situation. Parasympathetic output, associated with calming mechanisms, stimulates the iris sphincter to constrict, shrinking our pupils.

Dilating drops are anticholinergic agents, which block the effects of acetylcholine, the neurotransmitter released by parasympathetic nerve cells. Modern dilating drops are synthetic cousins of atropine, an extract of Atropa belladonna (also known as deadly nightshade). Atropine is a notorious poison, responsible for the famous quintet of signs that indicate ingestion of the toxin: “hot as a hare, red as a beet, dry as a bone, blind as a bat and mad as a hatter.”

One would only have to rub an eye after preparing this extract to discover its pupil-dilating effects. Apparently this property was exploited hundreds of years ago, particularly in Italy, by women who sought large pupils to create a doe-eyed appearance. The sight of one's beloved with pupils enlarged had the desired effect of communicating arousal.

Why don't tornadoes hit cities more often?

Could global warming make this event occur more frequently?

Joshua Wurman, president of the Center for Severe Weather Research in Boulder, Colo., whips up a response:

The glib answer for why tornadoes rarely strike urban areas is: cities are small. Look at Google Maps: the portion of the U.S. covered by urban and suburban areas is pretty minute. And the regions with peak tornado frequencies—from Texas up through Kansas and even out to the Southeast—are fairly open country.

It is very unusual that a tornado encounters a city, as happened in Atlanta this past March. When it happens, however, the storm need not be particularly strong to cause trouble. Tornadoes are rated 0 to 5 on the Enhanced Fujita (EF) scale: violent tornadoes are classified EF4 and EF5, significant ones EF2 and EF3. The tornado that went through Atlanta, which has been rated an EF2, did not raze downtown structures but did claim one casualty and cause millions of dollars in damages.

To address the second question, whereas one could be confident that the global temperature is going to rise, local effects—whether Atlanta or Topeka is going to heat up—are much less clear. On top of that, the effect of local temperature on tornado formation is unknown. Brazil is quite hot but does not have a lot of tornadoes. Oklahoma and Texas are very hot in summer, but those states see the most tornadoes in spring. So it is possible that climate change could shift the timing of the tornado season up, as spring's onset creeps into winter. Perhaps it will affect the geographic distribution of stronger tornadoes. But as for whether global warming will increase the number of tornadoes, making for more urban touchdowns, we may find out soon enough.

HAVE A QUESTION?... Send it to or go to