"As you know, we of Telfu are slightly ahead of you in chemistry. Yet there are things in chemistry that can not be solved without an advanced knowledge in the gravitic spectrum that Terra has exploited. Perhaps it was the lack of a channel in the gravitic that drove us into higher chemical development; but we are planet-locked until your people return to remove the block." "Go on," said Sandra impatiently. "I gather that you are in trouble of some sort?" "We are, indeed. A plague of ... ah, there is no word for it in Terran"--he switched to Telfan, "Andryorelitis," and back again to Terran--"which is an air-borne disease of the virus type. No inoculation has been discovered, and no immunity zone can be established. Telfu is in danger of halving the population." "Bad, huh?" "It is terrible. It strikes unknown. Its incubation period is several days, and then the victim gets the first symptoms. Nine days later, the victim is dead. Unfortunately, the victim is a carrier of andryorelitis during the incubation period, and therefore isolation is impossible." "Sounds like real trouble to me," said Sandra. "Will examination reveal it?" "Of course," answered Orfall. "But what planet can examine the population daily?" "I see the impossibilities. Then what do you hope? We have nothing that will combat it; knowing nothing of it in Sol would preclude any possibility. What can we do?" "To return to chemistry," said Theodi, "I will explain. Our chemico-physicists have predicted the combination of a molecule which will combat the virus selectively. It is a complex protein molecule of unstable nature--so unstable, unfortunately, that it will not permit us to compound it. We have used every catalyst in the book, and nothing works. Follow?" "I think so," said Sandra. "What keeps it from forming?" "As I said, it is very unstable. The atomic lattice appears to be structurally unsound. That happens in a lot of cases, you know. At any rate, we can make this molecule--and have made it successfully. But its yield is less than four ten-thousandths of one percent, and the residue precipitates out in an insoluble compound that can not be reprocessed." "Otherwise you would keep the process going until completion?" "Precisely. If reprocessing would work, we could leave the batch to cook until all of it went into combination. Or we could add fresh 'mix' to the processing batch and make the process continuous. But the stuff is not re-processable. We must complete each batch, and then go on a long process of fractionation to distill the proper compound out of the useless residue." "I can see that a process of that inefficiency would be bothersome," said Sandra.