For some moments none of us spoke. Alice recovered herself first.

"What is the matter with him?" she gasped.

I was incapable of finding a suitable reply, and stood, tongue-tied, staring foolishly at the old man. He seemed a little surprised at our behaviour.

"Dr. Harden," he said, "I am glad to see you. My daughter did not tell me you were coming."

His voice startled me. It was strong and clear. On my previous visit to him he had spoken in quavering tones.

"Oh, father, how do you feel?" exclaimed Alice, kneeling beside the bed.

"My dear, I feel extremely well. I have not felt so well for many years." He stretched out his hand and patted his daughter's head. "Yes, my sleep has done me good. I should like to get up for tea."

"But your eyes——" stammered Alice "Can you see, father?"

"See, my dear? What does she mean, Dr. Harden?"

"There is some discolouration of the conjunctivÆ," I said hastily. "It is nothing to worry about."

At that moment Alice caught sight of his finger nails.

"Look!" she cried, "they're blue."

The old man raised his hands and looked at them in astonishment.

"How extraordinary," he murmured. "What do you make of that, doctor?"

"It is nothing," I assured him. "It is only pigmentation caused—er—caused by some harmless germ."

"I know what it is," cried Alice suddenly. "It's the Blue Disease. Father, you remember the Perrys were telling us about it yesterday at lunch. They said it was all over Birmingham, and that they had come south partly to escape it. They must have brought the infection with them.""Yes," I said, "that is certainly the explanation. And now, Mr. Annot, let me assure you that this disease is harmless. It has no ill effects."

Mr. Annot sat up in bed with an exhibition of vigour that was remarkable in a man of his age.

"I can certainly witness to the fact that it causes no ill effects, Dr. Harden," he exclaimed. "This morning I felt extremely weak and was prepared for the end. But now I seem to have been endowed with a fresh lease of life. I feel young again. Do you think this Blue Disease is the cause of it?"

"Possibly. It is difficult to say," I answered in some confusion. "But you must not think of getting up, Mr. Annot. Rest in bed for the next week is essential."

"Humbug!" cried the old man, fixing his brilliant eyes upon me. "I am going to get up this instant."

"Oh, father, please don't be so foolish!"

"Foolish, child? Do you think I'm going to lie here when I feel as if my body and mind had been completely rejuvenated? I repeat I am going to get up. Nothing on earth will keep me in bed."The old man began to remove the bedclothes. I made an attempt to restrain him, but was met by an outburst of irritation that warned me not to interfere. I motioned Alice to follow me, and together we left the room. As we went downstairs I heard a curious sound proceeding from Mr. Annot's bedroom. We halted on the stairs and listened. The sound became louder and clearer.

"Father is singing," said Alice in a low voice. Then she took out her handkerchief and began to sob.

We continued our way downstairs, Alice endeavouring to stifle her sobs, and I in a dazed condition of mind. I was stunned by the fact that that mad experiment of ours should have had such a sudden and strange result. It produced in me a fear that was far worse to bear than the vague anxiety I had felt ever since those fatal tubes of the Sarakoff-Harden bacillus had been emptied into the lake. I stumbled into the drawing-room and threw myself upon a chair. My legs were weak, and my hands were trembling.

"Alice," I said, "you must not allow this to distress you. The Blue Disease is not dangerous."

She lifted a tear-stained face and looked at me dully.

"Richard, I can't bear it any longer. I've given half my life to looking after father. I simply can't bear it."

I sat up and stared at her. What strange intuition had come to her?

"What do you mean?"

She sobbed afresh.

"I can't endure the sight of him with those blue eyes," she went on, rather wildly. "Richard, I must get away. I've never been from him for more than a few hours at a time for the last fifteen years. Don't think I want him to die."

"I don't."

"I'm glad he's better," she remarked irrelevantly.

"So am I."

"The Perrys were saying that the doctors up in Birmingham think that the Blue Disease cut short other diseases, and made people feel better." She twisted her handkerchief for some moments. "Does it?" she asked, looking at me directly."I—er—I have heard it does."

An idea had come into my mind, and I could not get rid of it. Why should I not tell her all that I knew?

"I'm thirty-five," she remarked.

"And I'm forty-two." I tried to smile.

"Life's getting on for us both," she added.

"I know, Alice. I suggested that we should get engaged a short while ago. Now I suggest that we get married—as soon as possible." I got up and paced the room. "Why not?" I demanded passionately.

She shook her head, and appeared confused.

"It's impossible. Who could look after him? I should never be happy, Richard, as long as he was living."

I stopped before her.

"Not with me?"

"No, Richard. I should be left a great deal to myself. A doctor's wife always is. I've thought it out carefully. I would think of him."

After a long silence, I made a proposal that I had refused to entertain before.

"Well, there's no reason why he should not come and live with us. There is plenty of room in my house at Harley Street. Would that do?"It was a relief to me when she said that she would not consent to an arrangement of that kind. I sat down again.

"Alice," I said quietly, "it is necessary that we should decide our future. There are special reasons."

She glanced at me enquiringly. There was a pause in which I tried to collect my thoughts.

"Your father," I continued, "is suffering from a very peculiar disease. It is wrong, perhaps, to call it a disease. You wouldn't call life a disease, would you?"

"I don't understand."

"No, of course not. Well, to put it as simply as possible, it is likely that your father will live a long time now. When he said he felt as if his mind and body had been rejuvenated he was speaking the truth."

"But he will be ninety next year," she said bluntly.

"I know. But that will make no difference. This germ, that is now in his body, has the power of arresting all further decay. Your father will remain as he is now for an indefinite period."

I met her eyes as steadily as I could, but there was a quality in her gaze that caused me to look elsewhere.

"How do you know this?" she asked after a painful silence.

"I—er—I can't tell you." The colour mounted to my cheeks, and I began to tap the carpet impatiently with the toe of my boot. "You wouldn't understand," I continued in as professional a manner as I could muster. "You would need first to study the factors that bring about old age."

"Where did the Blue Disease come from? Tell me. I can surely understand that!"

"You have read the paper, haven't you?"

"I've read that no one understands what it is, and that the doctors are puzzled."

"How should I know where it comes from?"

She regarded me searchingly.

"You know something about it," she said positively. "Richard, you are keeping it back from me. I have a right to know what it is."

I was silent.

"If you don't tell me, how can I trust you again?" she asked. "Don't you see that there will always be a shadow between us?"

It was not difficult for me to guess that my guilty manner had roused her suspicions. She had seen my agitation, and had found it unaccountable. I resolved to entrust her with the secret of the germ.

"Do you remember that I once told you my friend, Professor Sarakoff, had succeeded in keeping butterflies alive for over a year?"

She nodded.

"He and I have been experimenting on those lines and he has found a germ that has the property of keeping human beings alive in the same way. The germ has escaped ... into the world ... and it is the cause of the Blue Disease."

"How did it escape?"

I winced. In her voice I was conscious of a terrible accusation.

"By accident," I stammered.

She jumped to her feet.

"I don't believe it! That is a lie!"

"Alice, you must calm yourself! I am trying to tell you exactly what happened."

"Was it by accident?"

The vision of that secret expedition to the water supply of Birmingham passed before me. I felt like a criminal. I could not raise my eyes; my cheeks were burning. In the silence that followed, the sound of Mr. Annot's voice became audible. Alice stood before me, rigid and implacable.

"It was—by accident," I said. I tried to look at her, and failed. She remained motionless for about a minute. Then she turned and left the room. I heard her go slowly upstairs. A door banged. Actuated by a sudden desire, I stepped into the hall, seized my coat and hat and opened the front door. I was just in time. As I gently closed the door I heard Mr. Annot on the landing above. He was singing some long-forgotten tune in a strange cracked voice.

I stood outside on the doorstep, listening, until, overcome by curiosity, I bent down and lifted the flap of the letter-box. The interior of the hall was plainly visible. Mr. Annot had ceased singing and was now standing before the mirror which hung beside the hatstand. He was a trifle unsteady, and swayed on his frail legs, but he was staring at himself with a kind of savage intensity. At last he turned away and I caught the expression on his face.... With a slight shiver, I let down the flap noiselessly. There was something in that expression that for me remains unnamable; and I think now, as I look back into those past times, that of all the signs which showed me that the Sarakoff-Harden bacillus was an offence against humanity, that strange look on the nonagenarian's face was the most terrible and obvious.