and Durkin
concocted as the explanation of their presence in the valley. But
evidently the Professor was too worried about the situation in which
he and his friends were, to question the two tramps very closely. In
fact, he seemed rather glad that he had two more pairs of hands to aid
him and he thanked Maget for his bravery.

They dispatched the great polywog as it tore its parent to bits, and
then the five men, the two Gurlones, Espinoza, Maget, and the limping,
cursing Durkin, retired to one of the shacks.

The living quarters of the Gurlones was quite elaborate. There were
many books on rough shelves, and there was a small bench filled with
glass phials and chemicals, though the main laboratory was in one of
the long buildings.

Professor Gurlone poured drinks for the five, and welcomed Durkin and
Maget as allies.

"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 moth