12 CORRELATION OF VITAL 



correlatable with ordinary physical forces, or whether it can 

 display itself independently of these.^ 



After discussing the many investigations which have been made 

 on this subject Gavarret summarised their results as follows : — "All 

 these experiments agree in showing that in the muscular system 

 of an animal which accomplishes actual work (such as raising 

 a weight, dragging a load, etc.) everything goes on as in an 

 ordinary steam-engine. While the muscle performs work, the heat 

 produced by the internal combustion becomes divided into two 

 complementary portions ; the one part appears as sensible heat, 

 and determines the temperature of the muscle, the other disappears, 

 so far as its existence in the form of heat is concerned, and, by the 

 intervention of the muscular contraction, becomes transformed into 

 mechanical work. The muscle is an animated machine, which, like 

 the steam-engine, utilises the heat in order to produce work : in 

 both cases there is necessarily an equivalence between the heat 

 which disappears, or is consumed, and the external work achieved." 

 In consequence of its origin, the energy manifested during the 

 contraction of the muscle is directly comparable with the energy 

 due to the elasticity of vapour when this is the motor power at 

 work, as in a steam-engine. Chemical change — combustion, in 

 fact — in each case, in muscle and in steam-engine alike, causes the 

 liberation of heat ; and in each case part of this liberated force is 

 capable of manifesting itself anew in the form of mechanical 

 energy. It matters not whence the heat is derived — whether it 

 comes from the decomposition of the recently assimilated food- 

 products, in the blood which circulates through the muscle, or 

 whether it proceeds from the liberated energy or sun-force that 

 may have been locked up for ages in the bowels of the earth, but 

 which is now set free by a process of combustion in the engine fire 

 — the result is the same, and in the muscle, as much as in the 

 steam-engine, we have to do with a machine in which the trans- 

 ference of heat into mechanical energy is capable of being effected. 

 The muscle, it is true, is a much more subtle kind of machine, 

 and the precise mode of its action is as yet hidden from us ; we 

 know not how it is — through what precise molecular changes taking 

 place in the substance of the muscle — that the heat which dis- 

 appears as heat, is, through the property of contractility, enabled to 

 reappear in the form of mechanical energy while the animal 



' For a full and admirable treatment of this question we must refer the reader 

 to pp. 120-194 of the work of Gavarret, already quoted. 



