“Or here!” With quick, nervous movements among his array of test-tubes, he turned a white solution to a wine color, and a light yellow solution to a dark brown.  He dropped a piece of litmus paper into an acid, when it changed instantly to red, and on floating it in an alkali it turned as quickly to blue.

“The litmus paper is still the litmus paper,” he enunciated in the formal manner of the lecturer.  “I have not changed it into something else.  Then what did I do?  I merely changed the arrangement of its molecules.  Where, at first, it absorbed all colors from the light but red, its molecular structure was so changed that it absorbed red and all colors except blue.  And so it goes, ad infinitum.  Now, what I purpose to do is this.”  He paused for a space.  “I purpose to seek—­ay, and to find—­the proper reagents, which, acting upon the living organism, will bring about molecular changes analogous to those you have just witnessed.  But these reagents, which I shall find, and for that matter, upon which I already have my hands, will not turn the living body to blue or red or black, but they will turn it to transparency.  All light will pass through it.  It will be invisible.  It will cast no shadow.”

A few weeks later I went hunting with Paul.  He had been promising me for some time that I should have the pleasure of shooting over a wonderful dog—­the most wonderful dog, in fact, that ever man shot over, so he averred, and continued to aver till my curiosity was aroused.  But on the morning in question I was disappointed, for there was no dog in evidence.

“Don’t see him about,” Paul remarked unconcernedly, and we set off across the fields.

I could not imagine, at the time, what was ailing me, but I had a feeling of some impending and deadly illness.  My nerves were all awry, and, from the astounding tricks they played me, my senses seemed to have run riot.  Strange sounds disturbed me.  At times I heard the swish-swish of grass being shoved aside, and once the patter of feet across a patch of stony ground.

“Did you hear anything, Paul?” I asked once.

But he shook his head, and thrust his feet steadily forward.

While climbing a fence, I heard the low, eager whine of a dog, apparently from within a couple of feet of me; but on looking about me I saw nothing.

I dropped to the ground, limp and trembling.

“Paul,” I said, “we had better return to the house.  I am afraid I am going to be sick.”

“Nonsense, old man,” he answered.  “The sunshine has gone to your head like wine.  You’ll be all right.  It’s famous weather.”

But, passing along a narrow path through a clump of cottonwoods, some object brushed against my legs and I stumbled and nearly fell.  I looked with sudden anxiety at Paul.

“What’s the matter?” he asked.  “Tripping over your own feet?”