558 GENERAL PHYSIOLOGY 



biogen-residue non-nitrogenous groups of atoms. The vital process 

 in muscle is the same, whether it draws its material from the 

 proteid of the food or from the carbohydrate and fat. 



The general validity of the idea here presented of the source of 

 muscle-energy will be more apparent after the problem of the 

 mechanics of the special changes of energy in contractile movements 

 has been examined in detail. 



d. Theory of the Movements of Contraction and Expansion 



Without considering singly the almost innumerable theories 

 that have been put forward regarding the mechanism of muscle- 

 contraction, we can distinguish among the more important views 

 expressed in the later physiology two essentially different groups. 

 There is general unanimity in the belief that muscle-energy has 

 its source in chemical energy, and, if the ideas here expressed upon 

 the vital process be accepted, there can be no doubt about this. But, 

 while according to some physiologists the mechanical energy of muscle- 

 work comes directly from the transformation of chemical energy, 

 according to others it comes by a roundabout way through heat. 

 The former view is defended by Pfluger (75, 1), Fick ('82, '93, 1) 

 and others, 1 the latter especially by Engelmann ('93). A theory by 

 the Gottingen philosopher, Elias Miiller ('91), which derives the 

 one kind of energy from the other indirectly, first through heat 

 and then through pyro-electricity, has not yet appeared in a com- 

 plete form. 



For the starting-point in our consideration we may best choose 

 Engelmann's thermodynamic theory of contraction. Engelmann 

 sees a difficulty in the direct derivation of muscle-work from 

 chemical energy in the following circumstances. If from the 

 amount of energy produced by muscle, upon the assumption that 

 this is afforded by the combustion of carbohydrates, and upon the 

 basis of a combustion heat of 4,000 calories per gram of carbo- 

 hydrates, the quantity of substance be computed that is necessary 

 to the work performed by the muscle in a single contraction, it is 

 found that this quantity is surprisingly small in proportion to the 

 mass of the muscle. Engelmann finds that approximately only 

 one four-millionth of the whole mass can be considered as yielding 

 the energy afforded in a single contraction. With the great 

 amount of water in the muscle, which he assumes at approximately 

 70 80 per cent., he regards it as incomprehensible how such an 

 enormous, passive mass can be put into motion by the direct effect 

 of the chemical energy of such a small quantity of effective sub- 

 stance working locally. He regards this as possible only when the 

 chemical energy is first transformed into heat, which can be dis- 

 tributed everywhere, and, therefore, is not limited in its effect to 

 1 Of. Verworn ('92, 1). 



