hydrin must be dissolved with distilled and sterilized water; this solution is poured into the measure, and the tube is again rinsed several times, after which the measure is filled up nearly to the mark. Ninhydrin dissolves sparingly in water, and in order to dissolve it quickly it must be heated a little. For this purpose it is best to stand the measure in the incubator. As soon as the solution is effected, the contents are cooled, and filled up to the mark on the flask.
The ninhydrin solution is not absolutely stable. It is liable to infection, and is also sensitive to the action of light. It may be kept in a brown flask, but this is not necessary so long as one prepares only 10 c.c. at a time, a quantity which is quickly used up.
After all the test-tubes containing 10 c.c. of the dialysate have been filled with 0.2 c.c. of the ninhydrin solution, a boiling-stick is placed in each. The latter is absolutelv essential, because only a very even ebullition will produce a properly comparable colour reaction. The boiling-sticks used in the trade are divided into segments about 10 cm. long; these must be boiled in distilled water, dried at 60° to 70°C., and kept in a tightly closed glass vessel. Boiling-sticks must not be stored in a damp condition; for on the one hand their use in this state may give rise to error, owing to the uneven amount of
