The social observer should enter these shadows. They form a part of his laboratory. Philosophy is the microscope of the thought. Everything desires to flee from it, but nothing escapes it. Tergiversation is useless. What side of oneself does one display in evasions? the shameful side. Philosophy pursues with its glance, probes the evil, and does not permit it to escape into nothingness. In the obliteration of things which disappear, in the watching of things which vanish, it recognizes all. It reconstructs the purple from the rag, and the woman from the scrap of her dress. From the cesspool, it reconstitutes the city; from mud, it reconstructs manners; from the potsherd it infers the amphora or the jug. By the imprint of a fingernail on a piece of parchment, it recognizes the difference which separates the Jewry of the Judengasse from the Jewry of the Ghetto. It rediscovers in what remains that which has been, good, evil, the true, the bloodstain of the palace, the inkblot of the cavern, the drop of sweat from the brothel, trials undergone, temptations welcomed, orgies cast forth, the turn which characters have taken as they became abased, the trace of prostitution in souls of which their grossness rendered them capable, and on the vesture of the porters of Rome the mark of Messalina’s elbowing.