“There is a poison which destroys life almost without leaving any perceptible traces. I know it well; I have studied it in all its forms and in the effects which it produces. I recognized the presence of this poison in the case of poor Barrois as well as in that of Madame de Saint-Méran. There is a way of detecting its presence. It restores the blue color of litmus-paper reddened by an acid, and it turns syrup of violets green. We have no litmus-paper, but, see, here they come with the syrup of violets.”

The doctor was right; steps were heard in the passage. M. d’Avrigny opened the door, and took from the hands of the chambermaid a cup which contained two or three spoonfuls of the syrup, he then carefully closed the door.