Three decades of persistent experiment and trial have firmly established the practical value of the cultural method for disclosing the presence of small numbers of mammalian tubercle bacilli in pathologic materials. I t now supersedes, in most respects, the more costly animal test which challenged the cultural method because of the high susceptibility of the guinea pig to small numbers of virulent human and bovine tubercle bacilli. The cultural method, however, proved superior in disclosing not only small numbers of virulent mammalian bacilli but also tubercle bacilli of low or moderate virulence and in being free from many uncertainties of the animal test. The most difficult problem to overcome, which the animal method surmounted easily, was the elimination of undesirable contaminating organisms without injury to the virulent tubercle bacilli. The early use of hypochlorites and, later, of the quickly acting caustic alkalies, despite their tissue-softening and solvent properties, left much to be desired in obtaining successful cultures in the presence of sparse numbers of bacilli. The desire for speed and for pure reagents led, in 1930, to the successful use of certain acids and to the recommendation of a pure crystalline simple acid, oxalic acid. The disadvantage of the acid, however, was that in spite of its suitable sterilizing effect on contaminants when properly used, it did not possess the liquefying or solvent properties of the strong alkalies, which, therefore, limited its usefulness when thick bulky specimens, such as sputum, were tested. Sodium hydroxide proved more satisfactory in this respect, but still possessed a number of undesirable features. The latter were obviated by the use of another weaker alkali, trisodium phosphate. Trisodium phosphate, which is also a tissue softener and penetrant, can be obtained in stable, pure crystalline form and can be maintained without deterioration for indefinite periods of time in suitable solution for use in destroying contaminants in tuberculous materials. In a previous communication it was pointed out that in 10 per cent solution (23 per cent Na3P04-12 H2O), trisodium phosphate can remain in contact with tubercle bacilli for up to one week at room temperature without destroying small numbers of tubercle bacilli, but it destroys the undesirable contaminants in sputum within twenty-four hours at 37 C , or within a period varying from several days to one week at room temperature. I t may also be placed in the receptacles used for collecting the specimen; this immediately prevents the development of molds and undesired contaminants. In ordinary specimens, such as sputum, urine, gastric washings and pus, the time required for destroying contaminants by