“I find that Gervaise’s window really had been broken, but that meant nothing; he might have done it himself in order to construct an alibi. Of the reason for Mademoiselle Bosworth’s torn robe, I could glean no trace; but behind my brain, at the very back of my head, something was whispering at me; something I could not hear, but which I knew was of importance.

“Then, as we drove away from the home, you mentioned the acid test. My friend, those words of yours let loose the memory which cried aloud to me, but which I could not clearly understand. Of a suddenness I did recall the scene at luncheon, how Mademoiselle Bosworth declared Mère Martin ate no meat for six months, and how angry Madame Martin was at the mention of it. Parbleu, for six months the little ones had been disappearing—for six months Madame Martin had eaten no meat, yet she was plump and well-nourished. She had the look of a meat-eater!”

“Still,” I protested, “I don’t see how that put you on the track.”

“No?” he replied. “Remember, my friend, how we stopped to interview the druggist. Why think you we did that?”

“Hanged if I know,” I confessed.

“Of course not,” he agreed with a nod. “But I know. ‘Suppose,’ I say to me, ‘someone have eaten the flesh of these poor disappeared children? What would that one do with the bones?’

“‘He would undoubtedly bury or burn them,’ I reply.

“‘Very good, but more likely he would burn them, since buried bones may be dug up, and burned bones are only ashes; but what of the teeth? They would resist fire such as can be had in the ordinary stove, yet surely they might betray the murderer.’

“‘But of course,’ I admit, ‘but why should not the murderer reduce those teeth with acid, hydrochloric acid, for instance?’

“‘Ah-ha,’ I tell me, ‘that is the answer. Already you have one whose hands are acid-stained without adequate explanation, also one who eats no meat at table. Find out, now, who have bought acid from some neighboring drug store, and perhaps you will have the answer to your question.’

“The Italian gentleman who keeps the pharmacy tells me that a lady of very kindly mien comes to him frequently and buys hydrochloric acid, which she calls muriatic acid, showing she are not a chemist, but knows only the commercial term for the stuff. She is a tall, large lady with white hair and kind blue eyes.

“‘It is Mère Martin!’ I tell me. ‘She is the “white lady” of the orphanage!’

“Then I consult my memory some more and decide we shall investigate this night.