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had killed a considerable number of people); restless after the scandal of his divorce from Emmy Fraatz. So Koch went from one end of the world to the other, offering to conquer plagues but not quite succeeding, trying to find happiness and not quite reaching it. His touch faltered a little. . . . And now Koch met Battista Grassi, and Grassi said to Robert Koch:

"There are places in Italy where mosquitoes are absolutely pestiferous—but there is no malaria at all in those places!"

"Well—what of it?"

"Right off, that would make you think mosquitoes had nothing to do with malaria," said Battista Grassi.

"So?”. . . Koch was enough to throw cold water on any logic!

"Yes—but here is the point," persisted Grassi, "I have not found a single place where there is malaria—where there aren't mosquitoes too!"

"What of that?"

"This of that!" shouted Battista Grassi. "Either malaria is carried by one special particular blood-sucking mosquito, out of the twenty or forty kinds of mosquitoes in Italy—or it isn't carried by mosquitoes at all!"

"Hrrrm-p,” said Koch.

So Grassi made no hit with Robert Koch, and so Koch and Grassi went their two ways, Grassi muttering to himself: "Mosquitoes—without malaria . . . but never malaria—without mosquitoes! That means one special kind of mosquito! I must discover the suspect. . . ."

That was the homely reasoning of Battista Grassi. He compared himself to a village policeman trying to discover the criminal in a village murder. "You wouldn’t examine the whole population of a thousand people one by one!" muttered Grassi. "You would try to locate the suspicious rogues first. . . .”

His lectures for the year 1898 at the University of Rome over, he was a conscientious man who always gave more lectures than the law demanded, he needed a rest, and on the 15th