194 SECTIONAL ADDRESSES 



which shows that oxygen and not carbon dioxide is concerned with the 

 conversion process. Thus COg can only result from oxidation (see also 

 Guy's Hosp. Reports, 85, p. 68) ; but oxygen has a two-fold function — 

 oxidation and conversion. It has been calculated that the heat of reaction 

 of this equation is 2 • i Gals, per grm. of fat, from which it follows that for 

 every litre of oxygen given out in the conversion of carbohydrate to fat 

 there is an absorption of heat of 3-93 Cals. The oxygen given out in 

 this conversion is used up in the oxidation of carbohydrate and fat, so 

 that a corresponding amount less is taken up from the atmosphere. 

 Equation 2 is based on Cathcart and Cuthbertion's analyses of human 

 fat. 



Now I litre of COj, produced in the oxidation of fat, is equivalent to 

 6-65 Cals. and in the oxidation of glycogen to 5 '125 Cals. On an 

 ordinary diet the CO2 output is constant with rise of quotient, and so if 

 there is a rise in the proportion of carbohydrate burnt there must be a 

 fall in the heat of combustion per litre of CO 2 with rise of quotient ; if 

 there is simultaneously a conversion of carbohydrate to fat there must be 

 a still further fall in the output of heat, as this is an endothermic reaction. 

 But on plotting the measured heat against the respiratory quotient this 

 is not found to be the case : it remains about the same. The only way of 

 expressing this theory to fit the facts is to say that on rise of quotient 

 there is an increasing combustion of carbohydrate relative to fat according 

 to the quotient, and simultaneously a conversion of fat into carbohydrate, 

 which seems absurd, but is really only a roundabout way of expressing 

 theory No. 2. Hence theory No. 3 falls out and No. 2, or the theory of 

 the constant combustion ratio, is left by exclusion. 



It must be admitted that this theory is not altogether unreasonable. 

 Many quantities associated with the human body have in health a more 

 or less constant value. The body temperature at rest varies within 

 comparatively small limits, and the same is the case with the hydrogen 

 ion concentration of the blood and the quantity of phosphocreatine broken 

 down in relation to muscular work ; while the amount of sleep remains 

 the same for an individual at any particular age. Why should not carbo- 

 hydrate and fat be burnt in constant proportion in the post-absorptive 

 condition in a normal healthy man. The story of Cain and Abel suggests 

 that the diet of primitive man was variable in its carbohydrate and fat 

 content, depending on his success in cultivation, when it would be mainly 

 carbohydrate, or hunting, when it would be mainly protein and fat. 

 Which is most likely, that the complicated metabolic processes resulting 

 in the actions of the heart, muscles and glands should be entirely at the 

 mercy of the individual's caprice (or luck) in his choice of food, or that 

 these processes should in the main run always along well-defined lines 

 of chemical and physical action, while any foodstuff taken in unusual 

 quantities is stored in some suitable form for future use, even though this 

 means a conversion of some kind ? Is it not reasonable to look on these 

 conversions of food as some of the earliest adaptations that the organism 

 has acquired in the course of evolution, and, as Dr. H. E. Magee has 



