i GENEKAL PHYSIOLOGY OF MUSCLE 89 



Engelmann's calculation the source of the energy necessary to 

 produce a contraction amounts to about four millionths of the 

 entire mass of the muscle. It is inconceivable to Engelmann 

 that the movement of the relatively enormous mass of inert 

 substance should be effected by the direct chemical attraction of 

 this minimal fraction of active substance, no matter what the 

 natural form or magnitude of the vibrations or the particular 

 arrangement of the few active molecules. He further objects that 

 the hypothesis of direct chemical attraction does not take into 

 account the fibrillary structure of the contractile apparatus, the 

 differentiation of the fibrils into isotropous and anisotropous 

 portions, the opposite variations in volume, form, refrangibility, 

 extensibility, etc., of these parts, and a number of other facts 

 which are in more or less open contradiction to it. 



Engelmann holds the thermodynamic theory propounded by 

 J. K. Mayer (1845), according to which the muscle is compared 

 with a steam engine which transforms the heat evolved in com- 

 bustion into mechanical work, to be far more probable. 



In reply to Sol way's criticism that the muscle works more 

 economically than any engine, Engelmann remarks that the 

 muscle is an apparatus whose combustible materials burn in 

 direct contact with the parts that perform the mechanical work, 

 so that it works under far more favourable conditions than Watt's 

 thermodynamic machine. 



Another, apparently more serious, objection to the theory of 

 the thermal origin of muscular energy put forward by Fick (1882), 

 and repeated by Gad, is that it is irreconcilable with the second 

 of Clausius' fundamental laws of thermodynamics. According to 

 this law, heat can only perform work when it passes from a warmer 

 body (A) to a cooler body (B*), and its potential is proportional to 

 the difference of temperature between A and B. So that before 

 we can assume that muscle works like a thermodynamic machine, 

 we must first prove that there is in it a marked difference between 

 A and B, or between the source of heat and the surrounding 

 medium. 



Fick held that this is not the case with muscle, which only 

 exhibits slight differences of temperature, proving conclusively 

 that it does not act as a thermodynamic motor. 



Engelmann replied to this objection that Pfliiger had already 

 pointed out in 1875 that body-temperature is only an arithmetic 

 mean which comprises innumerable very different temperatures 

 at innumerable different points of an organ, and that the molecules 

 formed in physiological combustion have, at least at the moment 

 of formation, an extremely high temperature, which they lose at 

 once by giving off heat to the cooler matter that surrounds them. 



Pfliiger 's conclusions in so far as muscle is concerned are con- 

 firmed, according to Engelmann, by the fact that the combustion 



