Ask Mr Brain...all will be explained

PUBLISHED : Tuesday, 05 October, 1999, 12:00am
UPDATED : Tuesday, 05 October, 1999, 12:00am

How can organs be transplanted? RUTH LO YING-WAI TWGHs S C Gaw Memorial College Since the first tissue grafts were carried out by Swiss surgeon Jacques Reverdin over 100 years ago, transplants have been the subject of a lot of medical research. The first successful kidney transplant was conducted at Loyola University in Chicago, United States, in 1950, and the first heart transplant was carried out by South African surgeon Christiaan Bernard in 1967.

Organ transplants allow people to enjoy a longer or better life than they otherwise would. Transplants vary from simple skin grafts and cataract replacement to heart, liver and kidney transplants. The main problem with organ transplants is rejection by the patient's immune system. Transplant organs come from another person, so they have foreign antigens - substances which trigger a reaction from the immune system.

If left unchecked, the body's immune system would react to the transplanted organ as if it were a disease and work all out to destroy the 'invader'. People undergoing organ transplants have to take im munosuppressive drugs to block the immune system's reaction until the transplant is secure. The problem is that by suppressing the immune system, many immunosuppressive drugs leave the patient susceptible to infection.

How do we see in 3D? WINNIE LAI Maryknoll Convent School Humans are able to see in 3D because they have binocular vision - both eyes face forward and see virtually the same image. The images from the right half of each eye goes to the right-hand visual centre in the brain's cerebral cortex, while the images from the left half of each eye goes to the left-hand visual centre. The brain then recombines the inverted images into a single image.

Because our eyes are set a few centimetres apart and facing forward, the image formed by each eye is slightly different. Although this type of vision has a small field of view, it enables us to judge distance and how solid an object is. This stereoscopic vision is common to predators, which need to be able to accurately gauge distance when hunting.

Animals which are prey usually have eyes set on the side of their head, which enables them to see in front and behind with 360-degree vision. But the images seen by both eyes are very different. Their field of vision overlaps only in a limited area directly in front and behind. This means their binocular, or 3D, vision is limited. Chameleons can swivel their eyes in all directions and look in two directions at the same time.

Films shot in 3D usually have two images - one red and one green - which were taken by lenses a few centimetres apart. Special 3D glasses for viewing them have one red lens and one green. The brain receives two separate red and green images, which it then recombines into one image, which appears to be 3D.