CONTRACTILITY AND PHOSPHORESCENCE. 187 



II. 



Among many theories that have been proposed by physi- 

 ologists, that of Engelmann ^ is most complete. This theory 

 Engelmann calls the " thermodynamic theory of muscular con- 

 traction," in which a muscle cell, or a bundle of muscle fibres, 

 is compared to a thermodynamic machine, not unlike our steam 

 engine. The theory was proposed by Julius Robert Mayer and 

 elaborated by Engelmann, from the careful study of the ana- 

 tomical, physiological, chemical aspects of the muscle cell, cilia, 

 unicellular forms, in short, in all organisms in which truly con- 

 tractile phenomena are exhibited. According to this theory, 

 the work tJie )?mscle accomplishes derives its energy from the heat 

 developed in the tissue, just as the work an engine accomplishes 

 is developed by the combustion of the fuel. The primary form 

 of contractile energy in the muscle is heat, which becomes 

 transformed into the mechanical work of contraction. 



The fact that the filamentous structures of the muscle are 

 really contractile elements had been demonstrated by Engel- 

 mann by separating the fibres from the muscle cell. The 

 isolated fibrils contract under a definite stimulus, thus refutino- 

 an idea entertained by some histologists, that the liquid portion 

 of the muscle cell is contractile. According to Engelmann, the 

 impulse given to the muscle cell causes the chemical change 

 in the non-contractile substance surrounding the contractile 

 filaments ; the latter are metamorphosed to such a high degree 

 that they do not readily undergo chemical changes. The chem- 

 ical disturbance started in the neighborhood and in the space 

 surrounding the contractile filaments takes the form of oxida- 

 tion chiefly, as shown by the nature of by-products. The heat 

 developed by the oxidation of thermogenic particles in the inter- 

 stices of contractile fibrils enables the latter to absorb more 

 water. And when an organized substance absorbs water, it 

 becomes thicker and shorter. This thickening and shortening 

 of the component fibres is the contraction of the entire cell. 



1 Engelmann, Th. W. tjber den Ursprung der Muskelkraft. Leipzig, 1S93. 

 " On the Nature of Muscular Contraction," Croonian Lecture before the Royal 

 Society of London, 1895. 



