“Thank you, Doctor.” She folded the form and put it in her purse.

On the point of ending the interview Dornberger hesitated. He knew, as most physicians did, that patients frequently had incomplete or wrong ideas about medical matters. When that happened with one of his own patients he was usually at pains to set them straight, even if it meant taking time to do so. In this case the girl had lost her first baby; therefore this second pregnancy was doubly important to her. It was Dornberger’s business to see that she had no anxieties.

She had mentioned Rh factors, and obviously the subject was on her mind. Yet he doubted if she had any real understanding of what was involved. He decided to take the time to reassure her.

“Mrs. Alexander,” he said, “I want you to be quite clear that, even though you and your husband have differing Rh blood types, it doesn’t mean there will necessarily be any problem with the baby. You do understand that?”

“I think so, Doctor.” He knew he had been right. In her voice there was a trace of doubt.

Patiently he asked, “Do you understand exactly what is meant by the terms Rh positive and Rh negative?”

She hesitated. “Well, I suppose not. Not exactly anyway.”

This was what he had expected. He thought for a moment, then said, “Let me put it as simply as I can. All of us have certain factors in our blood. And when you speak of a ‘factor’ you might say that it’s another name for an ‘ingredient.’ ”

Elizabeth nodded. “I see.” She found herself concentrating, adjusting mentally to take in what Dr. Dornberger was saying. For a moment she was reminded, almost nostalgically, of days in class. At school she had always taken pride in her capacity to understand things, to focus on a particular problem—absorbing facts quickly by excluding other things from consciousness. It had made her one of the brighter pupils. She was curious to know if she had retained the ability.

Dornberger continued, “Different human beings have different blood factors. The last time anyone counted there were forty-nine of these factors known to medicine. Most people—you and I, for example—have between fifteen and twenty of them in our own blood stream.”

Elizabeth’s brain clicked: question one. She asked, “What causes people to be born with different factors?”

“Mostly we inherit them, but that isn’t important now. What’s important is to remember that some factors are compatible and some are not.”

“You mean . . .”

“I mean that when these blood factors are mixed together, some will get along quite happily, but some will fight one another and won’t get along at all. That’s why we are always careful in blood typing when we give a transfusion. We have to be sure it’s the right kind of blood for the person receiving it.”

Frowning thoughtfully, Elizabeth said, “And it’s the factors that fight each other—the incompatible ones—that cause trouble? When people have babies, I mean.” Again her own classroom formula: be clear on each point before going on to the next.

Dornberger answered, “Occasionally they do, but more often they don’t. Let’s take the case of you and your husband. You say he’s Rh positive?”

“That’s right.”

“Well, that means his blood contains a factor called ‘big D.’ And because you’re Rh negative you don’t have any ‘big D.’ ”

Elizabeth nodded slowly. Her mind was registering: Rh negative—no “big D.” Using an old memory trick, she quickly made up a mnemonic:

If you haven’t got “big D”

Your blood’s a minus quantity.

She found Dornberger watching her. “You make it so interesting,” she said. “No one’s ever explained it like this before.”

“Good. Now let’s talk about your baby.” He pointed to the bulge below her waist. “We don’t know yet whether Junior here has Rh-negative blood or Rh-positive. In other words, we don’t know if he has any ‘big D.’ ”

For a moment Elizabeth forgot the mental game she was playing. With a trace of anxiety she asked, “What happens if he does? Does it mean that his blood will fight with mine?”

Dornberger said calmly, “There’s always that possibility.” He told her with a smile, “Now listen very carefully.”

She nodded. Her attention was focused again. Briefly, back there, she had let her mind become sidetracked.

He said deliberately, “A baby’s blood is always quite separate from the mother’s. Nevertheless, in pregnancy, small amounts of the baby’s blood often escape into the mother’s blood stream. Do you understand that?”

Elizabeth nodded. “Yes.”

“Very well then. If the mother is Rh negative and the baby happens to be Rh positive, sometimes that can mean our old friend ‘big D’ seeps into the mother’s blood stream, and he isn’t welcome there. Got it?”

Again Elizabeth said, “Yes.”

He said slowly, “When that happens, the mother’s blood usually creates something we call antibodies, and those antibodies fight the ‘big D’ and eventually destroy it.”

Elizabeth was puzzled. “Then where’s the problem?”

“There never is any problem—for the mother. The problem, if there is one, begins when the antibodies—the ‘big D’ fighters which the mother has created—cross over the placental barrier into the baby’s blood stream. You see, although there’s no regular movement of blood between mother and baby, the antibodies can, and do, cross over quite freely.”

“I see,” Elizabeth said slowly. “And you mean the antibodies would start fighting with the baby’s blood—and destroying it.” She had it now—clearly in her mind.

Dornberger looked at her admiringly. This is one smart girl, he thought. She hadn’t missed a thing. Aloud he said, “The antibodies might destroy the baby’s blood—or part of it—if we let them. That’s a condition we call Erythroblastosis Foetalis.”

“But how do you stop it happening?”

“If it happens we can’t stop it. But we can combat it. In the first place, as soon as there are any antibodies in the mother’s blood we get a warning through a blood-sensitization test. That test will be done on your blood—now and later during your pregnancy.”

“How is it done?” Elizabeth asked.

“You’re quite a girl with the questions.” The obstetrician smiled. “I couldn’t tell you the lab procedure. Your husband will know more about that than I do.”

“But what else is done? For the baby, I mean.”

He said patiently, “The most important thing is to give the baby an exchange transfusion of the right kind of blood immediately after birth. It’s usually successful.” He deliberately avoided mention of the strong danger of an erythroblastotic child being born dead or that physicians often induced labor several weeks early to give the child a better chance of life. In any case he felt the discussion had gone far enough. He decided to sum it up.

“I’ve told you all this, Mrs. Alexander, because I thought you had something on your mind about Rh. Also, you’re an intelligent girl, and I always believe it’s better for someone to know all the truth than just a part of it.”

She smiled at that. She guessed she really was intelligent. After all, she had proved she still possessed her old classroom ability to understand and memorize. Then she told herself: Don’t be smug; besides, it’s a baby you’re having, not an end-of-semester exam.

Dr. Dornberger was talking again. “But just let me remind you of the important things.” He was serious now, leaning toward her. “Point one: you may never have an Rh-positive baby, either now or later. In that case there can’t be any problem. Point two: even if your baby happens to be Rh positive, you may not become sensitized. Point three: even if your baby were to have erythroblastosis, the chances of treatment and recovery are favorable.” He looked at her directly. “Now—how do you feel about it all?”

Elizabeth was beaming. She had been treated like an adult and it felt good. “Dr. Dornberger,” she said, “I think you’re wonderful.”