ANIMAL HEAT 5&5 



appears as heat. Enough energy is transformed in twenty-four 

 hours in the heart of the colonel of a regiment of 1,000 men to lift 

 the whole regiment to the height of the mess-table, if it could be all 

 changed into mechanical work. Barcroft and Dixon have calculated 

 the energy of the heart's contraction on the assumption that it is 

 derived from the oxidation of a carbo-hydrate by the oxygen 

 absorbed by the organ. They concluded that the energy set free 

 in the heart of a dog weighing 12 kilos corresponds on the average 

 to 7-86 kilogramme-metres per minute, which is equivalent to 

 26 '6 calories in twenty-four hours. Allowing for the fact that the 

 heart of a small animal pumps more blood in proportion to the 

 body- weight than the heart of a large animal (p. 127), this result 

 agrees very well with that deduced from the work of the heart. 

 The work of the inspiratory muscles may be reckoned at 13,000 kilo- 

 gramme-metres, equal to 30*5 calories, and the heat produced by 

 them at, say, 90 calories. In sum, the muscular work cf the circula- 

 tion and respiration is responsible for the production of about 

 210 calories (without including the heat produced by the smooth 

 muscle of the bronchi and bloodvessels), or nearly one-twelfth of 

 the total production of a man doing ordinary labour. 



The glands, and then the central nervous system, rank after 

 the muscles, though at a great distance, as seats of heat-produc- 

 tion. The liver and brain (?) are the hottest organs in the body ; 

 and that this is not altogether due to their being well protected 

 against loss of heat is shown, in the case of the liver, by the 

 excess of temperature of the blood of the hepatic over that of 

 the portal vein. In view, however, of the exaggerated impor- 

 tance which some have given to these organs as foci of heat- 

 production, it may be well to point out that although many of 

 the chemical changes in the animal body are undoubtedly 

 associated with the setting free of heat (exothermic reactions), 

 other, and not less weighty and characteristic, reactions may 

 cause the absorption of heat (endothermic reactions) ; and it is 

 possible that some of the syntheses which many of the tissues 

 are capable of performing may be included in this latter category. 

 For example, when urea is decomposed so as to yield ammonium 

 carbonate (p. 438), heat is set free. We must assume that if 

 ammonium carbonate were transformed into urea in the liver, 

 an equal amount of heat would be, on the whole, absorbed. 

 So that the heat-production of an organ may depend, not only 

 upon the quantity, but also upon the quality, of its chemical 

 activity. In all the tissues, including the muscles, it is necessary 

 to assume that some of the energy transformed is expended in 

 so-called ' restitution ' processes that is, in replenishing the 

 store of nutritive material within the cells and in building up the 

 protoplasm. Claude Bernard observed an excess of 0*6 C. in 

 the temperature of the blood of the hepatic vein over that of 

 the portal during hunger, and as much as r6 at the height of 

 digestion, although at the beginning of digestion the portal 



