The problem of finding an agent or a method that will protect against the effects of whole-body irradiation has always been an attractive one, but in recent years many more investigators have been bending their efforts in this direction. The agents or methods brought to light by these investigations may be divided into three groups. To the first group belong those which have to be given prior to the irradiation, one of the best known representatives of this group being cysteine (1). The second group consists of agents or procedures that are used during irradiation; the most effective method of this group is the protection of the exteriorized spleen of the mouse by lead, discovered by Jacobson et al. (2). The third group of protective measures are effective when given post-irradiation. Among these are the intraperitoneal transplantation of spleens after irradiation which, as Jacobson (3) has shown, significantly increases survival of irradiated mice, and the injection of bone marrow following doses which are lethal to untreated mice and guinea-pigs, which is the subject of this paper. The discovery of the beneficial effects of spleen shielding against lethal doses of radiation raises the question whether a cellular or a humoral factor or both are involved in protection, since the shielded spleens of mice show abundant hematopoiesis following irradiation. Even the recent data of Jacobson et al. (3), dealing with the protective action of intraperitoneally transplanted spleens after lethal doses of irradiation, have not shown with certainty which factor or factors are involved, although the evidence appears to favor a humoral substance. The fact, however, that the shielded spleen of the mouse shows hematopoiesis makes it tempting to assume that seeding of hematopoietic elements to various organs and tissues from the spleen may play a role in the recovery process. If this be the case, then seeding with the cellular constituents of bone marrow, as by intravenous injection, should also be effective in hastening recovery. Previous experiments' however, do not seem to bear out such reasoning. Rekers and his associates (4, 5) treated dogs with intravenous injections of dog bone marrow after irradiation to 350 r. Only an equivocal improvement in survival rate was obtained. Talbot and Gerstner (6), using stock Sprague-Dawley rats (genetically not homogeneous) obtained an insignificant prolongation of mean survival time in rats injected intravenously with rat bone marrow after irradiation to 800 r. The failure of these experiments to yield any significant increase in survival, in comparison to irradiated control animals, may have been due to several factors, the most important of which may have been injection of non-viable cells and the use of genetically heterologous bone marrow.
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Lorenz et al. (1952) studied this question.