The strength of his limbs was leaving him.

He no longer felt any sensation in his cramped feet.

He measured the paralysis creeping up his legs inch by inch, driving the sharp pains before it--and then a groan of horror rose to his lips.
The light had gone out! As if that dying of the little yellow flame were the signal for his death, there came to his ears a sharp hissing sound, a spark leaped up into the blackness before his eyes, and a slow, creeping glow came toward him over the rock at his feet.
The hour--the minute--the second had come, and MacDonald had pressed the little white button that was to send him into eternity! He did not cry out now.

He knew that the end was very near, and in its nearness he found new strength.

Once he had seen a man walk to his death on the scaffold, and as the condemned had spoken his last farewell, with the noose about his neck, he had marveled at the clearness of his voice, at the fearlessness of this creature in his last moment on earth.
Now he understood.