Heretofore, it has not been possible to measure the heat production of individuals leading their usual lives, due to the unavoidable restrictions necessary to carry out either direct or indirect calorimetry. It is quite obvious that the movements of a subject in a calorimeter are sharply restricted by the capacity of the apparatus and, hence, prevent normal activity. On the other hand, the value of determinations based on indirect calorimetry depends on sampling in such a way that the expired air thus collected is really representative of the period, and there is no way of knowing whether this is the case. Further, the sampling necessarily requires the individual to be at rest for frequent ten minute periods and so disturbs his usual routine. The method which we are proposing is not hampered by either of these two restrictions.In an earlier paper (1) it was pointed out that the insensible loss of weight is roughly proportional to the heat production of the period, provided two sources of error are excluded; namely, first, there must be a proper relationship between the rate of heat production and the environmental conditions, and, secondly, the subject must be transforming a minimal amount of energy to mechanical work. In the previous paper it was also shown that the insensible loss of weight is the resultant of the weight of water lost by evaporation, the weight of exhaled carbon dioxide and the weight of absorbed oxygen. The relationship can be conveniently expressed as an equation:Insensible loss of weight = H20 + CO2 -02.
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