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Hot Rocks The worries that arise from bringing alien microbes to Earth ["Are We Ready for Alien Organisms?" March] ignore an obvious solution: Don't bring them to Earth. Since it is necessary to finance a new containment lab, it seems reasonable to set one up in orbit, perhaps on the space station. How much more contained can you get than the vacuum of space?

Keith Tallbe Massapequa Park, New York

Discover: And if the astronaut-scientists who examine the rocks in orbit become contaminated, do we just leave them up there?

While we should be taking extraordinary steps to quarantine extraterrestrial life that any probes may bring back, I believe the risks are overinflated. A past Discover article titled "The Arrow of Disease" [October 1992] explained why the American Indians—but not the Europeans—were decimated when the two peoples met. In a low-density population, a really deadly disease will kill off its host too quickly for the infection to spread, resulting in the organism's rapid extinction. If any Indians managed to survive, they eventually lost their defenses because the rate of infection wasn't high enough to make the defenses worth keeping. So any bug that survived could not have been too ferocious.

John Lee Stamford, Connecticut

Happy Hunting Grounds Regarding "Oh, Deer" [March], Erik Ness provides excellent and much-needed information about this very real crisis. Unfortunately, he does not even mention the obvious and bitterly debated part of the solution, namely to reintroduce the deer's natural population control predator: the wolf. Wolves are less dangerous to people than a forest full of trigger-happy hunters, cost nothing to keep them going, and keep the herd healthy by culling out the weak and the sick.

Jim Keene Seal Cove, Maine

As a hunter, I think it is refreshing to see a reputable publication include a scientific validation of the problems with deer overpopulation, but I would like to make one correction. Traditionally, hunters have preferred a very high population density to increase success rates. However, there is a wave of change called quality deer management, which is supported by a large percentage of hunters. Hunters now understand the benefits to themselves and the environment of having a healthier herd by keeping them below the carrying capacity of the land. This allows for a more natural and balanced age structure and healthier deer.

Johnnie Hennings Raleigh, North Carolina

Erik Ness identified an important problem, but the experts have overlooked a simple solution—one that's right there in the article. To preserve endangered plant species affected by overbrowsing, we need look no farther than the Fould's Creek hemlock grove in Wisconsin, where that accidental experiment in hemlock protection took place [see March issue, page 70]. Conservationists could, without too much cost or effort, create fenced-in bio-preserves that would permit deer-ravaged plant species to thrive. Fencing in carefully selected stands of existing species in small groves would permit these plants to survive in their geographic regions pending a longer-term solution to deer populations. We do this now with game corridors in the West, protecting avenues from predation (in this case, human development) so that isolated populations of wild game can stay connected. With a few fences and a bit of diligence, we could create pockets of plant diversity within game-management areas.

Ned Barnett Las Vegas, Nevada

Pressure Points I read "The Minus Touch" [The Physics of . . . Negative Pressure, March] with interest. While I am not an expert in this field, chemistry books have always indicated that water gets to the top of trees via osmotic pressure, which is caused by differences in concentration within the cells. It is not at all unusual to have an osmotic pressure of -20 atmospheres. Perhaps Karen Wright should have consulted a chemist.

Steven Engerer Associate Professor of Chemistry Valparaiso University Valparaiso, Indiana

Once again, Ms. Wright is mistaken. For one thing, she spent an entire article trying to relate two separate concepts in physics merely because they are both identified by the term "negative pressure." For another, this expression, as it applies to water flow through porous media, is a catchall term meant to be used for things that we usually cannot measure directly, such as the chemical, electrostatic, and molecular forces between a water-based solution and solids that give rise to capillary forces. If someone speaks of -2 atmospheres of hydraulic pressure in groundwater, he means the energy level of water that has been pulled by capillary forces to a level that corresponds to that much gravitational potential energy. Gravitational potential energy is what a rock has when you hold it two meters above the ground before letting it go. The water is not under negative pressure, because it is actually being held in place by other forces. And by the way, such pressures are usually measured not in absolute terms but in terms of their relative pressure when compared to that of the local atmosphere.

Don Baker Stillwater, Oklahoma

Chemical Alteration I suspect that if psychiatrist John Halpern examined fundamentalist, "tribal"-style religions, he would find the same success and failure in dealing with addiction as the Native American Church does—without peyote ["Peyote on the Brain," February]. Social and spiritual chemistry is the probable reason for success. Alcoholics Anonymous and other groups have deliberately re-created that tribal sense of community and community healing by banding together to form associations based on shared experience. I find it typical that some people, many of whom have not experienced addiction, cannot let go of the idea that the solution to chemical dependency is dependence on chemicals.

C.J. Lynde Courtenay, British Columbia

I thoroughly enjoyed the impartial and open-minded approach taken in "Peyote on the Brain" in describing the potential benefits and risks of using hallucinogens in the treatment of addiction. However, I would like to clarify a possibly misleading comment about our studies. Our research with N,N-dimethyltryptamine (DMT) was the first new research administering a hallucinogen to humans in the United States in 20 years. Accordingly, we were extraordinarily careful in our screening, supervision, and follow-up of our volunteers' drug sessions. We recruited only experienced hallucinogen users who were otherwise psychiatrically and physically normal. While there were, as John Horgan states, "adverse effects" in nearly half of our 60 volunteers, I included in this category any and all such responses. The vast majority were either minor or very brief, and none necessitated medical attention. Hallucinogens produce profound and intense psychological reactions, and even in the most stable individuals they may strain one's inner resources. Thus, both to minimize adverse reactions and optimize therapeutic ones, the proper setting, as articulated in John Halpern's work with the Native American Church, is critically important—perhaps, as the article alludes, even more important than the drug's effects themselves.

Rick J. Strassman Clinical Associate Professor of Psychiatry University of New Mexico School of Medicine Taos, New Mexico

Better Bred As one of the individuals contacted by Lisa Davis for her article on the genetics of purebred dogs ["That Dog Won't Hunt," April], I was disappointed that the article focused only on the negative aspects of the science and art of breeding these animals. What is missing is any mention of those commendable instances in which breeders of registered domestic dogs have received permission from such organizations as the American Kennel Club to open their studbooks to incorporate needed genetic material from unregistered dogs in many parts of the world. Similarly lacking is a mention of the highly successful selective breeding programs of such breeds as American and English foxhounds. Anyone familiar with these programs can testify that the pendulum is slowly but surely beginning to swing in the right direction.

I. Lehr Brisbin Jr. University of Georgia Aiken, South Carolina

It Takes a Village . . . Meredith Small ["How Many Fathers Are Best for a Child?" April] cites the Barí and other tribes as evidence that "the variety of family structures that are common in Western culture these days . . . may not be as dangerous to the social fabric as we are led to believe." The evidence is clear that there are different family structures that can work in a supportive culture. And while the reduction of shame attached to nontraditional families in Western culture is undoubtedly a positive step, it is also clear that the breakdown of the family has resulted in greater poverty for women and children, more homelessness, lower education levels, more health problems, and so on. Statements like Small's make it easy to dismiss these problems in the name of diversity. Until Western culture evolves to create adequate support structures for all families, we have a long way to go to catch up with the Barí.

Tim Goncharoff Santa Cruz, California

Enlightened Your April cover story "At the Speed of Light," by Tim Folger, did not give precedence to the paper titled "Superluminary Universe: A Possible Solution to the Initial Value Problem in Cosmology," by John W. Moffat. John, an emeritus professor of physics, published his pioneering work in 1993. Although some mathematical aspects of the theory were different from those in the subsequent paper by Andreas Albrecht and João Magueijo, the ideas and results based on a variable speed of light (VSL) in the early universe were substantially the same. In his book, Magueijo is careful to give credit to Moffat as well as to Moffat's subsequent publications on VSL. Tim Folger should have been just as generous.

Henry van Driel Department of Physics University of Toronto, Toronto, Ontario

Tim Folger: Professor van Driel is absolutely right—John Moffat did develop a varying speed of light theory several years before João Magueijo, and I regret not including that information in my story. My reason for not mentioning Moffat's work was that I wanted to devote an entire article to his career in a future issue of Discover, and I thought that a passing reference to his theory in a story that was mainly about Magueijo wouldn't be a satisfactory treatment of Moffat's ideas. I am truly sorry for the omission and hope to rectify it very soon.

Sour Grapes Because Discover gets high marks for accuracy, I was surprised to find an error in Vital Signs [April]. The photo caption on page 24 is incorrect. Streptococcus derives from the Greek words for "twisted" (streptos) and "berry" (kokkos). The "grape bunch"


refers to Staphylococcus.


Gerald S. Golden Philadelphia, Pennsylvania

Ageless Error In the May Bogglers, the answer to problem 5 of "Ageless Advice" is incorrect. The next number after 72 that works in the puzzle is 90, not 225. The number on the sign would be 16, and the children's ages would be 2, 5, and 9. By the way, I am a twin and my brother is younger than me (by seven minutes). Nonidentical twins can have different hair colors!

Keith Gillen Mountain View, California

Scott Kim: You're right, the answer is 90. Several readers corrected us, and a few noted that one twin can be younger than the other. But in our puzzle, the fact that the clue about the youngest child enabled the other parent to solve the problem means that the parents assumed that "youngest" ruled out twins. Comments about our Bogglers page can be e-mailed to



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