914 SPECIAL PHYSIOLOGY. 



2 to 1. The calorific work relates to the formation of heat; this is 

 generated, as we shall see, either in part, directly through the oxida- 

 tion of respiratory food, and, in part, indirectly from the ultimate 

 transformation of the mechanical work of the body into heat; or, ac- 

 cording to some, it is entirely derived from the latter source. The 

 nutritive work is the digestive, absorptive, assimilative, and secretive 

 work, liquefacient or solidifacient, often dialytic, attractive, or repel- 

 lent. The mental work is that which is involved in the operations of 

 the brain, acting as the bodily organ of sensation, emotion, and thought. 

 The volitional work of the brain, and the non-volitional work of the 

 spinal cord and ganglia, in controlling the voluntary and involuntary 

 muscles, cannot be separated from the external and internal mechani- 

 cal work performed by those muscles. Besides the electric work in 

 Man and in animals generally, special electric work is performed by 

 many animals, and photic phenomena are manifested by a few. 



In considering the relations between these forms of work in the 

 human body, and the source of the power in the oxidation of the food, 

 the following data, belonging to physical science, are usually employed, 

 the calculations being expressed in the French metrical system, which 

 so readily adapts itself to such uses. 



Measure of Heat, or Heat- Unit. 



The thermometer merely shows the relative temperature of solid, fluid, or 

 gaseous substances. The actual quantities of heat necessary to produce changes 

 of temperature, are determined by the apparatus known as a calorimeter ; and 

 the quantity needed to impart to a definite portion of water a definite warmth 

 is taken as a quantitative standard. Thus a quantity of heat which will raise 

 the temperature of 1 gramme (1 cubic centimetre, or 15.543235 grains) of water, 

 1 Centigrade (1.8 Fahrenheit), is named a heat-unit or calorie. Ten such 

 heat-units will raise the temperature of 10 grammes of water also by 1 C. ; but, 

 acting on smaller quantities of water, they will raise their temperatures pro- 

 portionally, as, for example, 5 grammes by 2 C., and 10 grammes by 1 C., 

 and so on, of 100's or of 1000's of heat-units. 

 



Mechanical Coefficient, and Mechanical Equivalent of Heat. 



Heat may produce work which is internal and direct, as in the liquefaction of 

 solids, e. (/.", in the melting of metals, and the turning of ice into water, or in the 

 conversion of fluids into vapor, as of water into steam, or in the mere expan- 

 sion of fluids or gases, as of mercury or air ; but heat may, also, act externally 

 and indirectly, as occurs in the employment of the expansive force of steam in 

 machines or engines of various kinds. The quantity of work performable by heat 

 is very remarkable. Thus, starting from the heat-unit previously determined, 

 it has been shown by Mayer, Joule, Clausius, and others, that such a heat- 

 unit, viz., the quantity of heat which will raise the temperature of 1 gramme 

 of water by 1 Centigrade, if utilized by being converted into mechanical work, 

 is equal to the lifting of the same weight of water, viz., 1 gramme, to a height 

 variously estimated at, from 421 to 433 metres, 424 metres being the number 

 usually adopted. Conversely, the same force will lift 424 grammes, 1 metre 

 high; or twice that number, viz., 848 grammes, half a metre ; or half that 

 number of grammes, viz., 212, to a height of 2 metres, or 106 grammes, 4 me- 

 tres, and so on for other quantities, larger or smaller. The mechanical coeffi- 

 cient of heat is therefore 424, and the mechanical equivalent of 1 heat-unit is 

 expressed as 424 metre-grammes. For larger weights, metre-kilogrammes are 

 used ; and it is here that the decimal notation of the metrical system is so use- 

 ful. Thus 1 kilogramme of water (1000 grammes) requires 1000 heat-units to 



