The British House of Lords has ruled that stem cells from fetuses can be used in medical research; nonetheless, we would all like a way of minimizing this source. Stem cells, of course, are only a few generations away from their creation. They express on their surface few or none of the histocompatibility molecules which bring the immune system down on them so heavily. Furthermore, the brain is a relatively privileged immunological site. That is why victims of Parkinson's disease, for example, can receive an injection of alien cells which will not be rejected. The cells may take their developmental cues from the brain around them, and reverse the effects of the disease.

So, says Daedalus, the best way forward would be to multiply stem cells in vitro, so that they could all be generated from just one fetus. DREADCO biochemists think that the medium is important. The best medium would be very 'young' — it should contain spinal fluid, and so forth, from very young organisms. It should be devoid of polarity cues, as this would encourage the cells to remain pluripotent and would repress any development or the establishment of gradients. A stirred system should do this.

So DREADCO biochemists are devising new media in which stem cells can be grown without deviating towards development. They are doping purely synthetic media with extremely young spinal fluid, brain fluid and so on, hoping that the cells will remain undeveloped for many generations. With luck these cells will be largely immune from immunological rejection. Thus in the brain they would take their developmental cues purely from the organ around them.

Indeed, says Daedalus, many simpler organisms, such as lizards, can regenerate legs or tails that become damaged or missing. They seem to be able to reverse cell development, and create new stem cells for the missing organs. With luck, plentiful human stem cells will enable humans to repair broken or missing arms and legs and wrecked tissues without the current trouble and limitations. All sorts of human damage could then be neatly repaired by allowing the cells to carry out the developmental plans which must be present even in the stump of a limb. Only the immune system, more active in the body than the brain, will have to controlled. And heart-transplant teams have already shown how to do this.