"We'll need every man we can get, if we are to cope with these great creatures," said old Gurlone. "The peons are too frightened to be of use. Luckily, it was a frog we came upon on the banks of the subterranean river. There is no telling how many more creatures of the same or greater size may be down there. We will have to destroy them, every one." Maget and Durkin shuddered. "Say," blurted Durkin, his face working nervously, "how the hell did that frog get so big? I thought I was seein' things, Professor." "No, no," said Professor Gurlone. "You see, the ore in the mine contains radium, that is, salts of radium. It is a pitchblende deposit, and it happens to be so rich in radium content that throughout the ages it has affected all the life in the cavern. The arid land surrounding the ore--this has been, generally, one of the characteristics of radium deposits--has kept most of the jungle creatures away, but underground beings such as reptiles, worms and frogs, have gradually become immune to the effects of the ore and have grown prodigiously and abnormally under the stimulation of the rays given off by the radium. "Now, this is nothing strange in itself, but never before has such a rich deposit been discovered, so that the amounts of radium available have been too small to really check its effect on growth in animals. That is our chief scientific object in coming here: we realized, from Senor Espinosa's description of the played-out silver mine he had, and from his loss of sight, that he had stumbled upon a valuable deposit of radium. It usually occurs with silver, that is, the uranium mother ore does, through the disintegration of which radium is formed. The content of radium per ton in this ore proved unbelievably rich: we were delighted. I have always suspected that the animal cell might be stimulated into abnormal growth by exposure to radium salts, for such a thing already has been hinted at in the scientific world. Not till our chance came here, however, has enough radium been available for the experiments." * * * * * Maget and Durkin listened with open mouths. Radium meant but vague things to them. They had heard of radium paint which shone in the dark on the dials of watches and clothes, but of the properties of the metal and its salts they were utterly ignorant. "That radium stuff is what makes the funny light in that mine, then?" asked Maget. "Exactly. The radio-activity of the elements in the ore give off the light. There are three rays, the alpha, beta and gamma, and--" The professor forgot himself in a lecture on the properties of radium. Durkin, breaking in, asked, slyly. "Is this radium worth as much as silver?" Young Kenneth Gurlone laughed, and even old Professor Gurlone smiled. "Radium is worth more than gold or diamonds or platinum. Its value is fabulous. We have five million dollars worth already, in the form of the chloride." "Whew," whistled Durkin.