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By means of certain microscopical methods areas from the middle third of trachea have been examined in children, died from various causes not connected with diseases in the pulmonary pathways. At birth in the mucous membrane of the trachea there is no lymphoid tissue. Its elements in a small amount appear at the initial stage of the suckling period. In two-month-old infants the first signs of lymphoid perinucleoli appear. During the early period of infancy the main regions of the lymphoid cells localization are clearly defined, in the area of some ducts of the tracheal glands including. In children, whose age corresponds to the first period of childhood, lymphoid accumulations have a pattern, resembling similar structures of the trachea in mature persons and the greatest concentration of cells, in comparison to the preceding groups of children in the ages examined.

Structural-functional organization of the lymphoid organs and functional state of the adrenals have been studied in animals, subjected to cold in early postnatal period, as well as changes of the parameters mentioned to a short and prolonged cooling in mature rats. For the animals increase in the thymus mass and in reproduction rate of lymphocytes in the thymus, spleen and lymph nodes is specific against the background of high corticosteroid secretion. When the control animals are kept in cold for a long time, after the phase of an acute stress, accompanied with hypercorticism and a pronounced lymphatic effect, during the period of an increased cold stability, the high secretion of glucocorticoid hormones is accompanied with a certain activation of thymus-dependent zones in the peripheral lymphoid organs. In the mature rats, subjected to cold at early ontogenesis both stress-reaction to cooling and rearrangement in the regulatory systems studied does not develop at adaptation to cold.

Amount and topography of small lymphoid nodules (SLN) have been studied by means of the quantitative method in flat total preparations of the small and large intestine obtained from 111 corpses of persons of both sex (from newborn up to old age). Total amount of the SLN in the large intestine wall in all age periods exceeds that of the SLN in the small intestine wall. From birth up to the period of the 1 childhood total amount of the SLN increases successively, reaching (51 +/- 14) X 10(2) in the small and (74 +/- 11) X 10(2) in the large intestine at the age of 4-7 years. Beginning from 8 years of age up to old age, total amount of the SLN decreases successively, to a more degree in the wall of the small intestine than in the large intestine. The arrangement density of the SLN in the large intestine wall essentially exceeds that of the SLN in the small intestine wall during the all age periods. From birth up to early childhood the arrangement density of the SLN increases and then gradually decreases both in the small and large intestine. This demonstrates that development of the SLN takes place during the first 4-7 years of the human life, in contrast to the lymph nodes and tonsils, their greatest development takes place during juvenile and adolescent age.

Basing on numerous facts, obtained during last years at investigation of the immune system organs, a definite idea has been formed on peculiarities of their structure during certain stages of human ontogenesis. The immune organs appear early in embryogenesis and by birth they have reached their morphological maturation. This is evident as formation of diffuse lymphoid tissue in lymphoid noduli, that can have germinative centers, where young cells of the lymphoid line are formed. The immune system organs develop especially quickly after birth during first years of the postnatal ontogenesis. The peak in development of the organs of immunogenesis, amount and size of the lymphoid noduli occurs during the childhood and adolescent age. Each immune organ has its peculiarities that are determined by their place in the organism, value and intensity of antigenic effect. Beginning from the adolescence and youth amount of the lymphoid tissue and lymphoid noduli in the organs decreases, in their place connective and adipose tissue grows out.