ONE FIGUREBoth congenital hypothyroidism (Benda, '47) and chronic starvation during childhood (Keys, Broiek, Henschel, Michelson and Taylor, 'SO) cause a serious and permanent impairment to bodily growth, and in either condition the basal metabolic rate may be depressed to as much as 40% of the normal level. Thyroid deficiency and inanition also have similar effects on the development of the nervous system for, in the rat, the growth of the brain is retarded, but less severely than that of the body. I n each case, therefore, the experimental animal has a central nervous system which is heavier than would be expected for a normal animal of the same weight (Hammett, '26a). Furthermore, the brains of both hypothyroid (Hammett, '26b) and starved (Donaldson, ' 11 ; Hatai, '04) rats contain less water in relation to their size than the brains of normal animals of the same age.This similarity of effect applies equally to the maturation of behaviour in the rat. Biel ('39) showed that chronic starvation retarded the time of first appearance of a number of automatic reactions and similar results have been reported in cretinous rats (Eayrs and Taylor, '51). These findings suggested that the changes in cortical structure which are associated with impairment to the maturation of behaviour in the cretin, such as reduced myelination (Barrnett, '48) and closer aggregation of cell bodies (Eayrs and Taylor, '51) might also occur in the starved animal.

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