We now come to one of the most interesting phases of the whole subject of radium--that is, the influence which its strange rays have upon animal life. Mr. Cleveland Moffett, to whom I am indebted for the facts of the following experiments, recently visited M. Danysz, of the Pasteur Institute in Paris, who has made some wonderful investigations in this branch of science. M. Danysz has tried the effect of radium on mice, rabbits, guinea-pigs, and other animals, and on plants, and he found that if exposed long enough they all died, often first losing their fur and becoming blind.
But the most startling experiment performed thus far at the Pasteur Institute is one undertaken by M. Danysz, February 3, 1903, when he placed three or four dozen little larvæ that live in flour in a glass flask, where they were exposed for a few hours to the rays of radium. He placed a like number of larvæ in a control-flask, where there was no radium, and he left enough flour in each flask for the larvæ to live upon. After several weeks it was found that most of the larvæ in the radium flask had been killed, but that a few of them had escaped the destructive action of the rays by crawling away to distant corners of the flask, where they were still living. But _they were living as larvæ, not as moths_, whereas in the natural course they should have become moths long before, as was seen by the control-flask, where the larvæ had all changed into moths, and these had hatched their eggs into other larvæ, and these had produced other moths. All of which made it clear that the radium rays had arrested the development of these little worms.
More weeks passed, and still three or four of the larvæ lived, and four full months after the original exposure one larva was still alive and wriggling, while its contemporary larvæ in the other jar had long since passed away as aged moths, leaving generations of moths' eggs and larvæ to witness this miracle, for here was a larva, venerable among his kind, that had actually lived through _three times the span of life accorded to his fellows_ and that still showed no sign of changing into a moth. It was very much as if a young man of twenty-one should keep the appearance of twenty-one for two hundred and fifty years!