The trace of tarnished copper, commonly called verdigris, poisoned the wholesome draught; a minute dose administered by stealth did incalculable mischief.  Behold the results of this criminal homoeopathy!  On the third day poor Cibot’s hair came out, his teeth were loosened in their sockets, his whole system was deranged by a scarcely perceptible trace of poison.  Dr. Poulain racked his brains.  He was enough of a man of science to see that some destructive agent was at work.  He privately carried off the decoction, analyzed it himself, but found nothing.  It so chanced that Remonencq had taken fright and omitted to dip the disc in the tumbler that day.

Then Dr. Poulain fell back on himself and science and got out of the difficulty with a theory.  A sedentary life in a damp room; a cramped position before the barred window—­these conditions had vitiated the blood in the absence of proper exercise, especially as the patient continually breathed an atmosphere saturated with the fetid exhalations of the gutter.  The Rue de Normandie is one of the old-fashioned streets that slope towards the middle; the municipal authorities of Paris as yet have laid on no water supply to flush the central kennel which drains the houses on either side, and as a result a stream of filthy ooze meanders among the cobblestones, filters into the soil, and produces the mud peculiar to the city.  La Cibot came and went; but her husband, a hard-working man, sat day in day out like a fakir on the table in the window, till his knee-joints were stiffened, the blood stagnated in his body, and his legs grew so thin and crooked that he almost lost the use of them.  The deep copper tint of the man’s complexion naturally suggested that he had been out of health for a very long time.  The wife’s good health and the husband’s illness seemed to the doctor to be satisfactorily accounted for by this theory.

“Then what is the matter with my poor Cibot?” asked the portress.

“My dear Mme. Cibot, he is dying of the porter’s disease,” said the doctor.  “Incurable vitiation of the blood is evident from the general anaemic condition.”

No one had anything to gain by a crime so objectless.  Dr. Poulain’s first suspicions were effaced by this thought.  Who could have any possible interest in Cibot’s death?  His wife?—­the doctor saw her taste the herb-tea as she sweetened it.  Crimes which escape social vengeance are many enough, and as a rule they are of this order—­to wit, murders committed without any startling sign of violence, without bloodshed, bruises, marks of strangling, without any bungling of the business, in short; if there seems to be no motive for the crime, it most likely goes unpunished, especially if the death occurs among the poorer classes.  Murder is almost always denounced by its advanced guards, by hatred or greed well known to those under whose eyes the whole matter has passed.  But in the case of the Cibots, no one save the doctor had any interest in discovering