I. Colonies of rats have been maintained for twelve generations on diets adequate (dietaryprotein energy: total metabolizable energy (NDP :E) 0.1) or marginally deficient in protein (NDP: E 0.068).2. In the malnourished colony, the proportion of 'small-for-gestational-age' offspring was ten times as high as amongst the well-nourished colony, growth was slow, sexual maturation delayed, especially in the females, and, when adult, both sexes were significantly lighter and shorter than adults of the well-nourished colony. Organs, other than the eye, weighed less than those of well-nourished 'age' controls, but when expressed relative to body-weight, the brain, pituitary, thyroid, adrenals, testes, thymus and eyes were larger, the pancreas unchanged and the kidneys smaller than those of the well-nourished 'age' controls. The relative weight of the liver showed little change, being slightly increased in the males and, like the ovaries, slightly reduced in the females. On a body-weight basis, the brains were about 50 yo heavier than normal, but in absolute terms were 5 3 . 5 % lighter than those of the wellnourished animals, the cerebellum (10.5 % lighter in males and 12.9 % lighter in females) being more severely affected than the cerebrum (4 yo lighter). 3.The young malnourished rats showed increased exploratory activity, transient head tremors and an increased sensitivity to noise, the latter being long-lasting if not permanent. When adult, they showed marked differences in behaviour and learning patterns and it was difficult to attract and hold their attention. In situations demanding a choice the animals were very excited, emitted loud squeals and tried to escape from what was clearly a stressful situation. However, a casual examination of the malnourished adults revealed a rather small, badly groomed, excitable rat without gross abnormalities.4. The findings are discussed in relation to changes found in malnourished human communities.There are many reports (see review by Platt & Stewart, 1971) indicating that protein-energy deficiency (PED) affects growth, development and reproduction as well as the chemical composition and morphology of many organs. Much effort has been expended on investigations into the effects of PED on brain development. The timing, duration and severity of the imposed deficiencies have varied greatly. Mothers have been maintained on inadequate supplies of food during gestation, the young have been given only limited access to the mother, the number of young suckled by one dam has been increased, animals have been given deficient diets only from weaning, and in some instances investigators have combined two or more of these techniques. Under any of these conditions the diet has to be severely restricted in quantity or quality, or both, in order to establish a deficiency during the critical periods of development. Except during periods of war or famine these are not the conditions existing in human communities in the depressed or non-industrialized areas of the world. More commonly the people...

I . Rats which have been maintained for ten to twelve generations on diets of low protein value were rehabilitated in utero (group P), from birth (group F) and from 4 weeks of age (group W).2. Group W showed little change in physique, behaviour or learning, indicating that for recovery to be effective refeeding must begin earlier.3. Group F just failed to attain full physical recovery (90%) whereas group P overgrew by 18.6% in weight and 8.5 O; in length. 4.In a test designed to evaluate learning ability rehabilitated rats of groups P and F were significantly less successful than normal rats, but more successful than rats of group W or rats of the original undernourished colony. .Rehabilitation for a further two generations in groups F and P corrected any residual physical and behavioural defects but produced no further improvement on the Lashley ( I 938) jumping platform.The changes produced in rats by several generations of marginal protein-energy deficiency have been reported earlier (Stewart, 1970;Stewart & Sheppard, 1971; Stewart e f al. 1975). There would appear to be a rapid adaptation in size and shape which stabilizes after two or three generations at a level probably controlled by the severity of the dietary deficiency. The adult males of the deficient colonyweighed approximately40 yo less than thewell-fedcontrols, and the females 30 yo less. Body lengths were reduced by 12 and 8 yo respectively and this was also the deficit in femur length. Brain weights were reduced by approximately 4-5 %.

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