Isolated Chromosomes

The chromatin threads, which we described briefly several years ago (1), have since then been studied carefully both morphologically and chemically. We now consider these microscopic threads of chromatin to be isolated chromosomes (2). From certain animal cells such masses of isolated chromosomes can be prepared that, with respect to quantity of material available, no special methods are required for chemical investigation. I t need hardly be said that interest in the chemical properties of this material is greatly enhanced by the knowledge that the material consists of chromosomes, for this provides the chemical studies with a background acquired by several generations of cytological investigation of chromosomes. In this paper the preparation of isolated chromosomes is described and evidence is presented that the bodies isolated are indeed chromosomes. Preparation of Isolated Chromosomes.--Chromosomes were first isolated from fish erythrocytes and their isolation from this source is simpler than from any other. Erythrocytes of the salmon and carp have been used. Of these the salmon is to be preferred, being a much larger fish, but for most investigators the carp is far more readily available. In some cities large, live carp can be had in the fish stores. Blood is withdrawn from the caudal vein with a syringe, mixed with oxalate, and centrifuged for 15 minutes at 5000 R.P.~. A white sediment, consisting of leucocytes, is obtained. The red cells are mixed with three volumes of 0.14 ~ NaC1 and centrifuged. This time the sediment consists of red cells. The red cells are well washed with saline. Finally, suspended in a large volume of saline, they are placed in a Waxing mixer for 4 minutes. All the cells and nearly all the nuclei are broken by this treatment, so that on centrifuging a clear red supernatant and a nearly colorless precipitate are obtained. The precipitate, suspended in saline, is placed in the mixer for 1 minute and centrifuged again. Washing is continued in this manner until the supernatant is colorless and at this time the precipitate is also nearly colorless. I t consists of chromosomes isolated from the erythrocyte nucleus (Figs. 5 and 6). The whole procedure is carried out in a cold room kept at about 1°C. The procedure that has just been described is nothing else than the first part 1