This book deals with one of the fundamental problems in the fields of biology and medicine, i. e. , the problem of adaptation of an organism to its environment. Essentially, adaptive responses enable animals and man to perform new tasks imposed by the environment and also to achieve timely avoidance of damage from environmental factors. Such are the roles of the defense response, adaptational reactions to high altitude and maximal loads, immunogenetic responses, etc. The author rightly views adaptive responses of the organism as reactions involving natural prophylaxis of disease, although processes of adaptation can also have detrimental consequences under certain conditions. It is, thus, understandable that problems of adaptation increasingly concern biologists, physiologists, and phy­ sicians. A number of important points distinguish this treatise from others in the field. Most researchers concerned with individual adaptation of human and animal organisms pay major attention to the dynamics of the gradual development of adaptation, i. e. , to gradual learning of new skills, training for endurance of new loads, or accomodation to high altitude. In the present monograph, abundant original and cited material is devoted to another problem: What is the concrete mechanism by which a nonadapted organism lacking resistance to a given factor is transformed into an adapted and resistant organism? In answering this question, the author concentrates mainly on the molecular basis of the adaptation mechanism.