The 21st century, it seems likely, will be a roller coaster of irregular design.

The ride will have long, boring stretches — dull and grudgingly accommodating, like the giant discount stores that will define the suburban landscape — then you’ll hit the steep climb, the sudden drops, the stomach-wrenching loops that’ll seem to go on past anything like fun…till you get to another long, boring stretch where you can retch in peace and, in time, wish for the chaos to break up the monotony again.

The GOOD -- Implants and new transplants. University of California, Davis scientists restored or vastly improved the eyesight of 10 of 14 patients without functioning corneas, by transplanting lab-grown corneas.

Two other bioengineered tissues are available — bioengineered skin is widely used to treat burns (is it used for cosmetic replacement of aging skin? Only a matter of time); bioengineered cartilage is used for knee injuries. On the purely artificial side, California’s Symphonix Inc.'s "Vibrant Soundbridge" surgical implant, is a mechanical device that’s implanted within the skull itself, mimicking the way sound is naturally transmitted through the ear canal. Some deaf people will miraculously be able to hear. I picture future anthropologists placing the date of uncovered 21st-century bones at a glance by noting the various little mechanical implants in the jumble of remains: "Hmmm…That looks like a Soundbridge rattling in the skull…non-allergenic plastic heart-valve under the ribs there…this doo-hickey between the hip bones is an Erector-1000 penile implant…definitely somewhere in the 2014 to 2017 range. Carbon dating? Nah."

The BAD -- you remember that Stanford University developed a chip that could link microelectronics and the axons of the brain. How socially good could such technology be, really, in the long run?

A closer, even VR-effective interface would be unthinkably addictive — would make it possible to live an alternative life to a greater degree than ever before. You could feel and sense what you do online, in special sites. How long before people pay to receive stimulation of their cerebral pleasure centers through online direct-interface brain chips in virtual-sex-and-drug sites? How long before people starve to death at their computers? How long, at this rate, before The Matrix comes true?

The GOOD -- Telomerase research has driven the stock on certain gerontological research companies up since researchers found that the enzyme, properly applied to human tissue, could significantly extend the life span of cells -- possibly the basis of a relative-immortality treatment. But…

The BAD -- scientists in Cold Spring, New York report that telomerase may not only extend life span, it may activate the c-myc oncogene — which would result in a little disorder called cancer. Ouch. Nature seems to plan for mortality — and whenever we reach for immortality, she always seems to have a counter-move….

The GOOD -- People like me, in their mid 40s, who have relatives who’ve died of Alzheimer’s — well, we tend to worry. We greet this one with the clicking of heels: An experimental vaccine that prevents and reduces Alzheimer’s. The vaccine, known as AN 1792, appears to create antibodies that prevent the formation of a sticky protein called amyloid plaques in mice that were genetically engineered to overproduce this sand in the gears of the brain of Alzheimer’s patients. Ireland’s Elan Corp. hopes to begin testing it on people later this year.

The BAD – If you already have Alzheimer’s, the brain damage is already done and the vaccine doesn’t reverse the damage. Its main use will be as a preventative. There’s still much work to be done on helping those already profoundly suffering from the disease.

The GOOD -- A possible cure for the allergies and asthma that torment millions of Americans. Researchers at Northwestern University and Harvard Medical School have decoded the complex interaction of two molecules central to allergic response. The discovery of how the antibody binds to the mast-cell receptor will lead to a new class of drugs that stop allergies before they start, preventing the cascade of released bodily chemicals that induce symptoms.

The BAD -- You may breathe easier, if you have allergies — but only if you can breathe at all. New England’s forests (for starters) may completely and utterly vanish in this century as a result of human-caused climate change. The government’s U.S. National Assessment on the impact of climate warns that 90 percent of the aspen maple and cedars would be eliminated by global warming. Rising temperatures are also expected to destroy alpine forests in the western U.S. Trees, you see, clean the air — and provide oxygen to breathe.

Let’s end on an up note: a GOOD -- Scientists at Ohio University, with a grant from the U.S. Department of Energy, are studying how algae, in the photosynthesis process, can absorb atmospheric pollutants, especially excess CO2 from coal-burning plants. The Ohio U team has proposed growing and harvesting the organisms directly in the exhaust gas from power plants -- talk about "greening" industry! Let’s hope the process works — otherwise… Better start practicing how long you can hold your breath.

Next time: The Good, the Bad and the Technology …