Studies in leukemia. VI. The induction of leukemia in AKR mice by means of cell-free brain filtrates of humans who died of leukemia.

MATERIALS AND METHODS Sections of brain were obtained at post mortem examination and as soon as possible were either frozen or processed. All autopsies were done within 24 hours of the death of the patient. The filtrates were prepared in the manner described elsewhere (1). Some idea of the uniformity of the human brain filtrates was achieved by nitrogen determi nation of samples of each filtrate. These were done by the micro-Kjeldahl technic and showed a range of from 1.2 mg. per cent to 5.2 mg. per cent. No correlation existed between nitrogen content and the induction of leukemia. Filtrates that failed to induce leukemia contained both the highest and lowest nitrogen values. The range of nitrogen con tent of those filtrates that did induce leukemia was from 3.2 mg. per cent to 4.5 mg. per cent. Control filtrates were prepared by heat in activa tion (65° C. for 45 minutes) of each of the human leukemic brain filtrates. In addition, fil-