"But," Roger stammered, "I've killed seven with it; that's not what I call a cure."
"Did you inject the seven with the dead culture first?" Lionel asked.
"No. Only myself and you."
"There you are," said Lionel. "You griffs make the discoveries, and haven't got the gumption to see them. My good Lord! It's as plain as measles. You inject the dead culture. That's the first step. That makes the trypanosomes agglutinise. Very well, then. You inject your serum when they are agglutinised; not before. When they are agglutinised, the serum destroys them, after raising queer symptoms. When they are not agglutinised the serum destroys you by the excess of what causes the queer symptoms. I don't understand those symptoms. They are so entirely unexpected. Did you examine the blood?"
"One cubic centimetre of the venous blood killed a guinea-pig in three hours."
"Yes, no doubt. But did you look at the blood microscopically?"
"No," said Roger, ashamed. "I looked at my sera for streptococci."
"You juggins!" said Lionel. "Yet you come out and land on a cure. Well, well! You're a lucky dog. Let's go in and look at our glands." Roger noticed that he walked with the totter of one newly risen from a violent attack of fever.
Four months later, the two men reached Shirikanga in a canoe of their own making. They were paddled by four survivors from the village. All the rest were dead, either of sleeping sickness or of the serum. Lionel had not discovered what it was in the serum which caused the fatal symptoms. It contained some quality which caused the streptococci, or pus-forming microbes, to increase; but, as far as he could discover, this quality was exerted only when the patient's blood contained virulent trypanosomes, or some other active toxin-producing micro-organisms in the unagglutinised condition. They cured four of the villagers. They might have saved more had they been able to begin the treatment earlier in the disease. They were not dissatisfied with their success. They "had powler't up and down a bit," like the Jovial Huntsmen. They had come to some knowledge of each other, and to some extension of their faculties.
Scientifically, they had done less than they had hoped; but more than they had expected to do. They had been the first to cure cases with animal serum. They had been the first to study in any way the effect of nagana upon the young of wild game, and to prepare (as yet untested) vaccine from young antelopes, quaggas, and elands. They had discovered a wash of Paris green and lime which destroyed the tsetse pupas. They had cleared some three miles of fly belt. They had studied the tsetse. They had surveyed the whole and excavated a part of the Zimbabwe. Lastly, they had settled the foundations of friendship between them.