Lavoisier's observation that his colleague Seguin consumed more oxygenafter eating a meal (Seguin and Lavoisier 1789) revealed a fundamental physiologicalproblem which has not been satisfactorily solved. A little over half acentury after this, the discovery that carbon dioxide prod~ction increases undersimilar circumstances (Scharling 1843) rendered more simple the experimentalinvestigation of the phenomenon, and then only a few years elapsed before boththe basal metabolism and the increase in heat production which superveneson feeding were defined. Edward Smith, after observing the rate of elimination? 'of carbon dioxide by human subjects under a variety of conditions, concludedthat" ... there is a normal (basal) level below which the system does not pass inhealth and wakefulness and which is tolerably uniform ... in complete abstinencefrom food . . . " and he expressed the view that " . . . foodstuffs may fitly bedivided into two classes, viz. those which excite certain respiratory changes andthose which do not." (Smith 1859a, 1859b.) .