“True, it is a terrible burden,” answered the searcher that was Roux, “but just because this serum has cured rabbits, I do not _know_ it will cure babies.... And I must know. I must find truth. Only by comparing the number of children who die, not having been given this serum, with the number who perish, having received it--only so can I ever know.” “But if you find out the serum is good, if it turns out from your experiment that the serum really cures--think of your responsibility for the death of those children, those hundreds of babies who did not get the antitoxin!” It was a dreadful choice. There was one more argument the searcher that was Roux could have brought against the man of sentiment, for he might have asked: “If we do not find out surely, by experiment on these babies, the world may be lulled into the belief it has a perfect remedy for diphtheria--microbe hunters will stop looking for a remedy, and in the years that follow, thousands of children will die who might have been saved if hard scientific searching had gone on....” That would have been the final, the true answer of science to sentiment. But it was not made, and who after all can blame the pitying human heart of Roux for leaving the cruel road that leads to truth? The syringes were ready, the serum welled up into them as he gave a strong pull at the plungers. He began his merciful and maybe life-saving injections, and _every one_ of the more than three hundred threatened children who came into the hospital during the next five months received good doses of the diphtheria antitoxin. Praise be, the results were a great vindication for the human Roux, for that summer, the experiment over, he told a congress of eminent medical men and savants from all parts of the world: “The general condition of the children receiving the serum improves rapidly ... in the wards there are to be seen hardly any more faces pale and lead-blue ... instead, the demeanor of the children is lively and gay!” He went on to tell the Congress of Buda-Pesth how the serum chased away the slimy gray membrane--that breeding place where the bacilli made their terrible poison--out of the babies’ throats. He related how their fevers were cooled by this marvelous serum (it was like some breeze blowing from a lake of northern water across the fiery pavements of a city). The most dignified congress of prominent and celebrated physicians cheered. It rose to its feet.... [Illustration: _à M^r. le D^r. Kruif Souvenir amical Dr. Roux. 18 Octobre 1923._] And yet--and yet--twenty-six out of every hundred babies Roux had treated--died, in spite of this marvelous serum....