For centuries the great minds of medical science puzzled over the importance of the cerebrospinal fluid. As far back as Hippocrates, it was thought that this "phlegm" that flooded the intracranial contents had pathological significance. However, not until the late 1800s, when Quincke introduced and popularized lumbar puncture, did physicians take an interest in the study of this fluid in relation to clinical illness. Since then a variety of techniques...