Greetings fellow Cyborgs."" That may well be the future form of address delivered by a home-grown, carefully processed president. ""Cyborg"" means man plus machine. It all started when some simian ancestor decided to extend his long-armed but limited capabilities by using a tool; since then we've come a long way and this intriguing study looks forward to the ultimate Cyborg--""a man-made man with immortal life."" This staggering possibility begins to seem reasonable as Mr. Halacy cites scientific accomplishments. Examples--kidney transplants from chimpanzees to men; brains removed from monkeys and kept alive for periods up to 18 hours in the laboratory, not only alive but able to hear and respond to sight and sound stimuli; artificial creation of life; the human embryo conceived in a test tube which lived for 27 days until its life was terminated; Naval volunteers trained to breathe helium and oxygen at seven times the customary pressure; research on DNA, drugs, suspended animation, etc. Mr. Halacy makes no judgments on whether or not we are overextending ourselves; he sticks to facts and probabilities. Well-written, fascinating, disquieting.