"Did you employ the Gettler test?"
"Yes—inconclusive. The blood in the left side of the heart had a slightly lower concentration of sodium chloride than the blood on the right. If that difference had been pronounced, you could call it fair evidence of inhalation of fresh water, but it was too slight. I don't attach any significance to it."
"Could the lack of a positive finding be significant?"
"I don't think so. It's a good test, but plenty of things may confuse it. For instance, a drowning may occur from pharyngeal shock—a spasmodic throat contraction that causes asphyxia before much water is inhaled. Logically still a drowning death, but no water to speak of, so there goes your Gettler test."
"You looked of course for evidence of aconitine poisoning?"
"Only in a limited sense, sir. Aconitine doesn't leave gross traces for post-mortem, it's a job for the toxicologist, a chemical job. Since I knew Dr. Ginsberg would be working on it, I simply bore it in mind, prepared what he needed, and kept my eyes open. I can say under oath that I found nothing inconsistent with aconite poisoning having occurred shortly before the drowning. But the actual immediate cause of death was, in my opinion, asphyxia due to immersion, in other words drowning."
"Doctor, will you give the jury a description of the effects of aconitine in a lethal or near-lethal dose?"
"Frankly, sir, I'll be drawing on textbook knowledge, because this is the only case I ever encountered. Homicide by aconite is decidedly rare. So is suicide." Callista looked up, not to the doctor who dutifully faced the jury and would not look at her, but searching the rows of spectators. "Aconitine will cause numbness, tingling in the mouth, also in the fingers, possibly cramps in arms and legs. There's marked salivation, nausea, burning sensation in stomach and throat." Edith moved in her seat, and smiled, and tried to call in silence: I'm here. But Callista's eyes, searching, immense, drowned, passed over her. "A slow, irregular, weak pulse is characteristic, with rapid shallow breathing, muscular weakness, a general collapse. Nausea and vomiting are usual; sometimes there are convulsions. The poison depresses the medullary centers of the brain, but the cerebrum is hardly affected, which means the mind stays pretty clear until the coma that may supervene at the end." Callista's eyes found what they were seeking. It would not be her mother, Edith knew: Victoria Chalmers sat over at Edith's left. "Those symptoms I've described begin soon after aconite is taken. I believe death, when it occurs, usually comes in about four hours—but it can happen in a matter of minutes."
Edith wished not to turn her head; she felt instead an unwillingness, distaste, reluctance to learn what would be written in the face of Jim Doherty. But she could not help it. Knowing where he was seated, she was forced to turn until a sidelong look gave her the image of him, completing at that instant the sign of the cross, his eyes lowered, his lips moving. But the man beside him was watchful, interested, attentive, probably missing none of the testimony.
"What is the minimum lethal dose, Dr. Devens?"