Effects of Radiation on Hemopoiesis

Abstract

A consideration of the effects of radiation on the hemopoietic tissues brings one into a controversial field. This is necessarily so, since various modes of subjecting the blood and the hemopoietic tissues to radiation have been used. Further, results in one species do not always agree with those in other species and hence confusion is frequently caused by an attempt to apply to one species what has been found to occur in another. Difficulties of the above type are so commonly encountered in the older literature on the subject that it has been decided not to include here any survey of this literature. Excellent reviews are available for those who want them. One of the most recent is that by Shields Warren in 1942. The types of radiant energy under consideration in this discussion are either electromagnetic energy waves, such as roentgen and gamma rays, or particulate matter having mass, such as alpha and beta particles, protons, and neutrons. While the former are devoid of mass (other than energy mass) and electrical charge, they may for convenience be considered as bullets of energy called quanta. The alpha particle is the nucleus of the helium atom, having a unit positive charge of two and a unit mass of four. The beta particle (electron) has a negative charge of one and a unit mass of 1/1840. The proton is a component of all atomic nuclei and comprises the entire mass of the hydrogen nucleus. It has a unit positive charge of one and unit mass of one. The neutron is a component of all atomic nuclei with the exception of the hydrogen nucleus. It is neutral in charge and has a unit mass of one. The positron and mesotron are omitted from this discussion for simplification. An unstable atomic nucleus (one having excess energy) may return to a more stable state by the release of energy in the form of an alpha particle, an electron, a proton, a neutron (neutron only during fission process), a gamma ray, or by a combination of several of these forms of energy. An unstable atom may release its excess energy in the form of light, heat, or roentgen rays, or by a combination of two or more of these forms. Materials being subjected to these radiations may be considered as being bombarded with quantas of energy without mass and by particulate matter having both mass and energy. All living cells, whether of man, animal, or plant, are capable of injury from these various types of radiant energy. The extent, location, and type of injury which may be sustained are dependent upon the kind of radiation under consideration, its physical properties, its mode of application, (whether external or internal), its intensity, duration of exposure, and the character and function of the cells of the species of animal or plant being subjected to irradiation. In other words, the degree and character of the biological changes resulting from irradiation are dependent upon many complicating factors and often subject to difficulties of interpretation.