Rapid concentration of proteins and electrolytes from frozen urine by centrifugation.

serum to thaw completely during centrifugation. Further experiments have shown that protein and electrolytes can be removed rapidly from frozen serum or urine by centrifugation, at relatively low speeds with little or no visible evidence of thawing. Part of the sample (25 ml.) of urine from a nephritic dog was placed in the barrel of a '20 ml.' plastic syringe suitably plugged at the exit and frozen at -6°C. overnight. A 5 ml. glass bottle was placed in the bottom of a 100 ml. centrifuge bucket and the plastic syringe barrel with frozen urine placed on top after removing the stopper from the exit. Both containers were suitably wrapped. The unit was then centrifuged for 1 minute at 3,500 r.p.m. at room temperature, when 3-47 ml. of yellowish fluid was obtained from the glass bottle and a cylindrical tightly fitting cast of frozen colourless ice was shaken from the syringe barrel. The fluid concentrate and a sample of the original urine were analysed for protein by the Biuret method and for sodiurn using a Beckman spectrophotometer. The ease with which protein and sodium can be removed from frozen urine or serum is due to the fact that water freezes first and the substances suspended or dissolved therein are trapped in the lattice work of ice crystals in a concentrated form and are removed by centrifugal force. A critical temperature must obviously be reached when all the constituents are frozen and this techniquc would not then operate.