Doctors in training are generally taught lumbar puncture at the bedside, at least “in my day”, using a “see one, do one, teach one” approach. The volume of cerebrospinal fluid (CSF) to be taken was elaborated to me as follows: three drops for bacteriology and three drops for biochemistry, and if the first aliquot is bloody then another three drops for bacteriology to try to differentiate traumatic trap from blood in the …