“Here on Grass, however, a virus evolved which, as part of its process of reproduction, creates an enzyme, an isomerase, which converts L-alanine to D-alanine. L-alanine is the usual form. D-alanine is the mirror image, the isomer, and it is virtually nonexistent anywhere we know of. I’m quoting Lees exactly. She’s said it a hundred times, so I know I’ve got it right.” She stopped for a moment to drink, to watch Rigo watching her. He gestured vaguely, telling her to go on.
“After hundreds of thousands of years, the virus became widely dispersed here, in the living cells of all plants. As the plants died, the D form was released into the environment. Over time, here on Grass, the D form became as common as the L form. That’s the important fact, Rigo. Here on Grass, both D-alanine and L-alanine are floating around, ubiquitous. We can’t breathe or drink this coffee or eat anything grown here without taking in some of both—along with the virus.
“The minute we stepped off the ship from home, we were infected. The virus is in the air, in the dust, in the water. Lees says we probably had viruses in almost every cell of our bodies within minutes. The virus needs a co-factor in order to reproduce, however. A kind of activator. D-alanine is the co-factor. The viral protein binds to this co-factor, and then it converts L to D, very rapidly. However, the virus works both ways. It can also bind to L-alanine, and when it does, the viral protein converts D to L.
“Binding to D-alanine takes almost no time here on Grass because there’s so much D-alanine around. Someplace like Terra, where there are maybe only a few accidental molecules, it could take a long, long time. That’s why the plague was so slow to start elsewhere. It’s also why there isn’t any plague here on Grass. As soon as we started breathing on Grass, all our cells got supplied with D and L both.
“So, here on Grass, the virus inverts L, which we need in order to live, to D, which our bodies can’t use. However, since both D and L are plentiful, it turns both forms around simultaneously, and each of our cells finds enough L-alanine to go on living. On other planets there was little or no D-alanine to start with. When L was reversed, only D was left, and the cells couldn’t use it. When human cells died, the viruses escaped into neighboring cells in their immediately infective stage, and the process was repeated. People got sores that spread. Bandages, wash water, anything that touched the body served as a source of infection, and the dead cells provided the co-factor for newly infected cells.”
“But not here,” Rigo said stiffly.
“Not here. On Grass, both D-alanine and L-alanine are plentiful; our cells survive. The virus’s life cycle is interrupted, the cells die naturally. People come here and get infected and go away, never knowing it….”
“And it was spread by bats?” Father Sandoval asked.
“Lees says the bats don’t use alanine. It’s only one of a number of amino acids, and the bats just don’t use it. However, the blood of other animals has alanine in it. The bat doesn’t need it, so the viruses and the co-factors exist in the bat’s blood bladder. When bats die and dry, their insides are powdery with virus-rich material, as packed with viruses and with co-factors as a puffball is with spores. Dead blood-sucking bats are about as good a carrier as you could get.”
“You haven’t said what the cure is,” Father Sandoval said, finding on Rigo’s face an expression which reinforced his own mood, one of frustrated anger. One could not be angry that a cure had been found; one was, however, annoyed at the way it had been found.
“The cure?” She looked up, puzzled. “Well, of course, Father. I thought that was self-evident. All that’s needed is to spread massive quantities of D-alanine around. Small doses are no good. If somebody gets small doses of D, it will bind to the enzyme and they’ll die. But if they get massive amounts, more than is needed to bind, then there will be equal mixtures of L to D and D to L conversion. And of course. Semi in 2 found that it was extremely easy to make. They just used the virus to manufacture it out of L-alanine.”
Father Sandoval shook his head. “It sounds so simple the way you describe it. But the Arbai couldn’t cure it, as wise as they were?” He would not believe in their wisdom, no matter what Father James had said. Furthermore, he felt the church would disbelieve in their wisdom as well. Doctrine, as he knew it, had no room for other children of God.
“Perhaps they died faster than we did. My informant doesn’t know.
“Your informant?” Rigo said, his voice ugly. “A foxen! Horses weren’t enough for you, Marjorie?”
She frowned at him warningly, repressing her sudden anger. “Don’t, Rigo. If you are ambassador to Grass, you are ambassador to them, as well. They aren’t animals.”
“That is not for you to decide,” the priest said, echoing her anger with a sullen fury of his own. “That is a question for the church, Marjorie. Not for you. They may be intelligent and still be animals. Your relationship with them may be a serious error. I caution you!”
“You what?” she asked, incredulous. “You what?”
“I caution you. On pain of excommunication, Marjorie. Do not continue in this mindless adulation of these creatures.”
She looked at the priest, betraying nothing. His face was red, then white. His hand, resting upon the table, was clenched. Rigo looked much the same. They had been discussing her again. Talking over how she was to be controlled, no doubt. Her
