The next time someone says, “I smell danger in the air,” that might literally be true — and the odor might be coming from you.

At the tip of the noses of mammals, including humans, is a ball of nerve cells known as the Grueneberg ganglion, named after Hans Grueneberg, the scientist who described the structure in mice in 1973.

Grueneberg thought it was just a nerve ending. Only in last few years, after scientists devised strains of mice that glow green under fluorescent light, did they deduce that the Grueneberg ganglion is a component of the olfactory system. But they still did not know what the ganglion smelled.

In the Aug. 22 issue of the journal Science, researchers at the University of Lausanne in Switzerland report that they have figured it out, at least for the green-glowing mice.

All sorts of organisms, including plants, insects and mammals, release “alarm pheromones” when they sense danger; the pheromones waft through the air to warn others. Very little is known about the alarm pheromones of mammals other than that they exist. Scientists have not identified the compounds; they do not know where in the body the pheromones are produced. Nonetheless, the Lausanne scientists could collect the pheromones by simply stressing mice and sucking up the air around them.

When other normal mice were exposed to the danger-scented air, they froze in their tracks. But mice whose Grueneberg ganglia had been excised did not notice anything wrong and continued to wander around their cages without a care in the world.

Scientists Create Blood From Stem Cells

Scientists have used embryonic stem cells to generate blood -- a feat that could eventually lead to endless supplies of type O-negative blood, a rare blood type prized by doctors for its versatility.

"We literally generated whole tubes in the lab, from scratch," said Robert Lanza, chief science officer at Advanced Cell Technologies.

People usually require blood transfusions that match their own blood type: A mismatch can be fatal. Type O-negative can be safely transferred into anyone, but is only possessed by about 7 percent of the population, leaving supplies perpetually short.

The new technique, devised by Lanza and colleagues at the Mayo Clinic and University of Illinois, is still preliminary. Its safety hasn't yet been proved in animals, much less humans.

But because blood cells are short-lived and cannot divide, there's reason to believe that stem cell-derived blood cells could pose fewer complications than other therapeutic stem cells, which can divide unpredictably.

"The beautiful thing is that you start with one line, expand them indefinitely and generate as many as you want," said Lanza. "It's a literally inexhaustible source of cells for therapy."

Lanza's team allowed a small culture of embryonic stem cells -- naturally capable of becoming any other type of tissue in the body -- to divide until it numbered a few billion cells. These they treated with a chemical cocktail that coaxed the cells into whatever type they wanted: A, B or O. If they'd started with a type O-negative line, said Lanza, they could just as easily have made that, too.

Tests showed the blood cells to be identical to each other, and able to carry oxygen as efficiently as their natural counterparts.

The Red Cross described the work, published today in Blood, as "pioneering." However, they warned against premature celebration.

"At this stage, the work is very promising, but has not progressed to the stage where the cultured cells are fully equivalent" to natural cells, said the organization in a statement. "Much more work will yet be needed before this becomes a practical reality."

The most pressing uncertainty is safety: Embryonic stem cells are sometimes unpredictable and can develop genetic mutations during chemical reprogramming, leading to future side effects.

Blood cells, however, don't have any DNA -- they lose their nuclei as they develop from stem cells -- and don't divide, instead being broken down by the body when their four-month life cycle ends. That, said Lanza, should reduce the possibility of complications.

"You don't have to worry about anything lifelong," he said. "They'll be gone no matter what."

The ethics are potentially problematic, as embryonic stem cells ultimately originate in an embryo that is destroyed during their harvest -- a process that some religious conservatives equate with murder.

But Lanza said his technique could also work with stem cells produced by de-differentiation, a new and ethically trouble-free process during which adult cells regress into an embryonic state.

De-differentiated cells have a tendency to go cancerous -- but because blood cells are DNA-free, said Lanza, they could be safe in this particular application.

If Lanza's technique works, it will be a boon wherever blood transfusions are needed, but especially in places where type O-negative blood is not immediately available, such as emergency rooms and battlefields.

"There's always a great demand for type O blood," said Red Cross spokeswoman Molly Dalton. "It's always a worry that we don't have enough."

Scientists Say We Can See Sound

Turning conventional neuroscience on its head, new research suggests the human visual system processes sound and helps us see.

Here's the basics of what was Neuroscience 101: The auditory system records sound, while the visual system focuses, well, on the visuals, and never do they meet. Instead, a "higher cognitive" producer, like the brain's superior colliculus, uses these separate inputs to create our cinematic experiences.

The textbook rewrite: The brain can, if it must, directly use sound to see and light to hear.

The study was published last week in the journal BMC Neuroscience.

Monkey hear, monkey see

Researchers trained monkeys to locate a light flashed on a screen. When the light was very bright, they easily found it; when it was dim, it took a long time. But if a dim light made a brief sound, the monkeys found it in no time — too quickly, in fact, than can be explained by the old theories.

Recordings from 49 neurons responsible for the earliest stages of visual processing, researchers found activation that mirrored the behavior. That is, when the sound was played, the neurons reacted as if there had been a stronger light, at a speed that can only be explained by a direct connection between the ear and eye brain regions, said researcher Ye Wang of the University of Texas in Houston.

The study presents the first evidence that a sensory cell can process an alternative sensation, said head researcher Pascal Barone of the Université Paul Sabatier in Toulouse, France, who discovered a contender for the anatomical connection in 2002.

Emergency broadcast

The discovery likely explains the tremendously quick reactions of most animals, including humans, to stimuli that cue multiple senses, such as a rustling tiger or a honking bus.

Especially in the corners of the visual field, where eyesight is poor, the ears take up the slack and stimulate the visual system, Barone said.

An extra benefit, Wang explained, is the early visual system’s spatial precision, something higher brain regions fudge in favor of prioritizing our central gaze. By sending sound inputs directly to our image processor, the auditory system can avoid playing telephone with time-sensitive information.

Extra-sensory power

The discovery is likely unrelated to the rare experience of synesthesia, a bizarre condition experienced by a few people who can feel, hear and taste colors. In synesthesia, for example, more complicated sensations combine at later stages of brain processing, so that just the mention of a color, a letter or a shape can automatically trigger the perception of a certain note.

What most excites Barone about the new findings is the potential for "cortical plasticity" in sensory areas.

For example, the blind, by definition, do not use the visual system to see. But they can, this research suggests, use it to hear. This may explain how blind people develop such advanced hearing skills and, similarly, why the deaf often possess superior sight, said Barone.

The primary visual system is also directly activated by touch – perhaps helping us slap that mosquito before it stings.