The description of sequelae of nutritional deficien cies was equally oversimplified. Obviously, a disease like rickets, which affected hard tissues--the skeleton- had irreversible consequences. Destruction or alteration of tissues, such as in cancrum oris or severe xerophthal mia, was equally permanent and easily observed. Other models were beriberi or scurvy, where, by contrast, the vitamin treatment seemed to restore the individual to the completely normal status quo ante. Most nutritionists were therefore little prepared intellectually for the series of suggestive findings con cerning nutrition and mental development which has been the highlight of nutritional research in the past decade: the discovery that there are irreversible gaps in mental development not correlated with obvious permanent somatic lesions which follow acute malnutrition during the develop ment of the young infant. Furthermore, not only are ex isting somatic instruments--physical examination, the scale, and the measuring tape--inadequate to detect such intellectual and behavioral deficits, but some of the current psychological instruments, bound to traditions of Western culture, are often poorly adapted to measure fine differences in psychological development among poor populations. These initial discoveries have stimulated important methodological advances, ranging from better staining techniques for the study of fibers connecting brain neurons to better tests for the study of cognitive development.