RELATIONS OF HEAT TO FORCE. 459 



culations have been made showing the conversion of foot-pounds or kiio- 

 grammetres into heat-units, but mechanical difficulties have thus far pre- 

 vented the actual conversion of heat-units into their equivalents in foot-pounds 

 or kilogrammetres. As a matter of reasoning, however, it is assumed that if 

 a certain number of foot-pounds or kilogrammetres be equal to a certain 

 number of heat-units, the reverse of the equation is true ; but in the applica- 

 tion of this law to animal physiology, it is always by a conversion of heat- 

 units into foot-pounds or kilogrammetres. The experiments on which the 

 law rests have been made by converting foot-pounds or kilogrammetres into 

 heat-units. 



In work by machinery a very large proportion of the force-value of fuel 

 is dissipated in the form of heat. This is well illustrated by Landois. If a 

 steam-engine burning a certain quantity of coal, but doing no work, be 

 placed in a calorimeter, the heat produced can be measured. If, now, the 

 engine be made to do a certain work, as in raising a weight, the heat, as 

 measured by the calorimeter, will be less and the work done is found to be 

 very nearly proportional to the decrease in the measured heat (Him). It is 

 estimated by Landois, that of the heat produced by the body, one-fifth may 

 be used as work. In the best steam-engine, it is possible to use only one- 

 eighth as work, seven-eighths being dissipated as heat. 



Many elaborate and careful estimates have been made of the mechanical 

 work produced by the human body. The basis of such calculations is more 

 or less indefinite, and the reduction of the work to foot-pounds or kilogram- 

 metres is difficult and inexact. Even the general statement, that of the 

 heat-units produced by the body, four-fifths remain as heat and one-fifth is 

 converted into work, must be regarded as merely approximate. 



In the animal organism, a part of the potential energy of the tissues may 

 be converted into force by voluntary effort. In fevers, an abnormally large 

 proportion of the potential energy of the organism is converted into heat, 

 and it is not possible to use much of this energy as force. These and other 

 peculiarities of living bodies, as regards the production of heat and force, 

 are difficult of explanation. In the essential fevers, the conditions which 

 involve the abnormal production of heat finally consume the substance of the 

 tissues. They involve especially an increased production of carbon dioxide 

 and urea and not to any great extent the formation of water. If heat-pro- 

 ducing alimentary substances and alcohol can be introduced and consumed, 

 the tissues are thereby proportionally saved from destruction and degenera- 

 tions. 



