INCOME AND EXPENDITURE OF ENERGY 663 



In one of Atwater's ' severe work ' experiments the work done in 

 twenty-four hours had a heat- equivalent of 1,482 calories (equal to 

 over 630,000 kilogram me- metres). The total heat-production (in- 

 cluding the equivalent of the work) was 9,314 calories. It is not 

 difficult to show that the greater part of the metabolism and heat- 

 production of a man doing ordinary work is accounted for by the 

 contraction of the voluntary and involuntary muscles. 



Even in muscles completely at rest metabolism goes on, and some 

 heat is produced. In resting frogs, newts, and snakes, the rate of heat- 

 production per gramme of tissue is about 0*5 gramme-calorie per hour 

 with a room temperature of 20 C., or about a third of that of a resting 

 man (Hill). Of course, this must be above the heat-production of 

 muscles of these poikilo thermal animals absolutely at rest. For not 

 only must the active heart and glands contribute something, bu the 

 muscles of frogs lying huddled in a micro-calorimeter not only maintain 

 the normal tonus, but are certainly liable to contract actively from 

 time to time. By analyzing the gases of the arterial and venous blood, 

 Zuntz compared the oxygen consumption and carbon dioxide produc- 

 tion in the hind-legs of dogs when the sciatic and anterior crural nerves 

 were divided and intact. In both cases the muscles were at rest in 

 the ordinary sense. But in the second experiment the central ' tonus ' 

 (p. 889) was preserved, while in the first it was abolished. In one 

 experiment in which the nerves were intact the oxygen consumed 

 amounted to i'22 c.c., and the carbon dioxide produced to 1*32 c.c., 

 per kilo of tissue per minute. In the experiment in which the nerves 

 were severed, the corresponding numbers were 0-68 c.c. for the oxygen, 

 and 0-63 c.c. for the carbon dioxide. Although it is probable, from 

 the results of Chauveau and Kauffmann already referred to (p. 266), 

 that these figures are too low for the normal resting muscle, they still 

 demonstrate that, even in the absence of innervation from the central 

 nervous system, the metabolism, and therefore the heat-production of 

 the muscles, are by no means negligible; 0*68 c.c. of oxygen per minute 

 corresponds to 40-8 c.c. per hour, or more than one-tenth of the oxygen 

 consumption per kilo per hour of a fasting dog lying at rest (Zuntz). 



If the work of the heart is taken as 16,600 kilogramme-metres in 

 twenty-four hours (p. 138), the total heat produced by this organ will 

 be equivalent (on the assumption that it converts one-third of its 

 energy into work) to about 50,000 kilogramme-metres, or not much 

 less than 120 calories, since, practically, the whole work is expended 

 in overcoming the friction of the vessels, and finally 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 con- 

 cluded that the energy set free in the heart of a dog weighing 12 kilos 

 corresponds on the average to y86 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 propor- 

 tion to the body- weight than the heart of a large animal (p. 139), 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 



