ATOMIC MEDICINE it became evident that age, strain and species were factors that influenced the results. The effectiveness of several subcellular fractions of spleen homogenates prepared by the Schneider-Hogeboom techniques was then tested. The experiments conclusively showed that there was no restorative effect connected with the mitochondria, microsomes or soluble supernatant fractions. The restorative effect was found only with the cell meleus fraction. Since relatively few intact cells were found on stained smears of the nucleus fraction, it was believed that their experiments strongly sup- sy Re SAMISUE 224 i ' were common. A British group (Barnes and Loutit) have made a series of contributions on the nature of the restorative action of splenic implants and homogenates. Initially, they confirmed the effectiveness of splenic homogenates. Next, they showed that immunization of one strain of mouse (CBA) bystrain A material prevents protection; whereas, short-lived protection of CBA mice could be obtained by use of strain A material in nonimmune mice. In general, their experience was the same as Cole ef al. in that freezing, thawing, irradiation, and formalin-treatment inactivated the principle. Their studies, extensively confirmed for bone marrow, showed that the restorative principle of intact CBA mice spleens could be preserved when the spleens are equilibrated with glycerol serum andstored at —70°C. for as long as 83 days. Recently very signifieant studies, incantrovertible when con-idered together, have been reported independently by several different laboratories eiiaseptdinRaere <= 1, alentLunt)Sab yngYe Tye hereite cannesla have shown that DN Aase and trypsin inactivate the material, as does distilled water extraction under various conditions. Since enzymes are believed not to attack living intact cells, these experiments were interpreted as indicating that the active principle is associated with DNA and not necessarily with living cells. These contentions argued strongly for the noncellular concept. It was thought carly that studies with heterologous marrow might provide the definitive answer to the question of whether cell transfer is involved in these protective phenomena. Lorenz and Congdon, and Congdon and Lorenz reported that homologous and heterologous ground bone favorably modify lethal radiation injury in the mouse. Transplanted homologous bone developed bone marrow, but heterologous bone transplants did not show bone marrowformation. The same investigators reported protection of some strains of mice by intravenous injections of rat bone marrow emulsion from certain strains of rats. They interpreted the bone and bone marrow transplant studies as evidence in favorof the existence of a humoral factor. Cole et al. protected mice with rat bone marrow. Late deaths after 2 weeks ales at Woot males we ported the concept that the restorative effect was noncellular and associated with the nucleoproteins. Further studies on the splenic homogenates 3 & 5 y