Traditionally, the biological sciences have focused their attention on the whole organism, on organs as functional units, or on individual tissues in the quest for knowledge of mechanisms controlling development. Alternatively, the biochemist and endocrinologist have explored enzymes and metabolic pathways seeking the same goals. Improved methodologies now permit convergence of these approaches in the study of cells as fundamental units of structure and function. As this review has emphasized, the preliminary results are encouraging and exciting.

The concept of critical periods in development has been repeatedly emphasized. Systematic exploration of the effects of imposed nutritional variables on cell ploidy, the appearance or disappearance of enzyme systems, and the production and/or functional expression of hormones will shed light on imprinting effects of early deficiencies on the growing organism. Sex and age differences in these parameters are most thought provoking, as is the potential application of cell methods to diagnosis or monitoring progress of childhood diseases. Particularly exciting are the studies seeking to explain the consequences of malnutrition on nerve cell development, an understanding of which may perhaps identify a biological basis for subsequent behavioral abnormalities. A potentially fruitful area for study is the aging process, with emphasis on improved understanding of cellular changes associated with maturation and decline in cellular function.

Acceleration of progress in this field will depend on refinements in methods for counting cells and estimating cell size or functionality. Special attention needs to be given to DNA as the index for cell function in the light of recent questions concerning the nature and location of DNA in different cells. More direct measures of cell function are needed inasmuch as large cells may not in fact be more functional cells.

Comparability of findings from experimental animals to developmental processes in subhuman primates and humans need clarification. The need for new experimental models (including invertebrates) for research on cellular aging is particularly pressing. The adaptation of cell culture techniques to nutritional problems is another promising area for expanding research.

The cellular approach to nutrition promises new explanations for nutritional influences on development. The data presently available partly explain why nutritional insults at a given time have permanent repercussions throughout life. These and future findings will be significant beyond the laboratory setting, having impact upon clinical diagnosis as well as on the design and implementation of improved nutrition service programs.

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