In an instant he was back again.

“Now, Doctor,” he said, “I’m going to perform a very delicate test on this man.  Here I have the alternating city current and here a direct, continuous current from the storage-batteries of the cab below.  Doctor, hold his mouth open.  So.  Now, have you a pair of forceps handy?  Good.  Can you catch hold of the tip of his tongue?  There.  Do just as I tell you.  I apply this cathode to his skin in the dorsal region; under the back of the neck, and this anode in the lumbar region at the base of the spine—­just pieces of cotton soaked in salt solution and covering the metal electrodes, to give me a good contact with the body.”

I was fascinated.  It was gruesome, and yet I could not take my eyes off it.  Torreon stood blankly, in a daze.  Craig was as calm as if his every-day work was experimenting on cadavers.

He applied the current, moving the anode and the cathode slowly.  I had often seen the experiments on the nerves of a frog that had been freshly killed, how the electric current will make the muscles twitch, as discovered long ago by Galvani.  But I was not prepared to see it on a human being.  Torreon muttered something and crossed himself.

The arms seemed half to rise—­then suddenly to fall, flabby again.  There was a light hiss like an inspiration and expiration of air, a ghastly sound.

“Lungs react,” muttered Kennedy, “but the heart doesn’t.  I must increase the voltage.”

Again he applied the electrodes.

The face seemed a different shade of blue, I thought.

“Good God, Kennedy,” I exclaimed, “do you suppose the effect of that mescal on me hasn’t worn off yet?  Blue, blue everything blue is playing pranks before my eyes.  Tell me, is the blue of that face—­his face—­is it changing?  Do you see it, or do I imagine it?”

“Blood asphyxiated,” was the disjointed reply.  “The oxygen is clearing it.”

“But, Kennedy,” I persisted; “his face was dark blue, black a minute ago.  The most astonishing change has taken place.  Its colour is almost natural now.  Do I imagine it or is it real?”

Kennedy was so absorbed in his work that he made no reply at all.  He heard nothing, nothing save the slow, forced inspiration and expiration of air as he deftly and quickly manipulated the electrodes.

“Doctor,” he cried at length, “tell me what is going on in that heart.”

The young surgeon bent his head and placed his ear on the cold breast.  As he raised his eyes and they chanced to rest on Kennedy’s hands, holding the electrodes dangling idly in the air, I think I never saw a greater look of astonishment on a human face.  “It—­is—­almost—­natural,” he gasped.

“With great care and a milk diet for a few days Guerrero will live,” said Kennedy quietly.  “It is natural.”

“My God, man, but he was dead!” exclaimed the surgeon.  “I know it.  His heart was stopped and his lungs collapsed.”