384 MUSCULAR ACTION 



more carbon dioxide is liberated from it. We know that, as often 

 happens in protoplasm, the chemism of metabolism gives rise to at least 

 three sorts of kinetic energy: movement, heat, and electricity, for these 

 may be measured and variously studied. 



If we start out with the fact that it is chemism undoubtedly which 

 liberates these energies, we have the basis of the chief various theories 

 of muscle-action. To one (Engelmann) it seems clear enough that 

 the chemism gives rise to heat, which, by causing imbibition of sarco- 

 plasm, brings about the contraction. Another "school" (Pfliiger, 

 Bernstein, Verworn, Fick) supposes that the chemism directly, i. e. y 

 without the intervention of heat, alters the two differing substances in 

 such a way that the isotropic one swells into the anisotropic. A recent 

 group of thinkers (Miiller, Loeb) suppose that electricity is involved in 

 causing the contraction. To others (e. g., Weber), the chemism seems 

 to alter the natural elasticity of the myoids or fibrils, making them 

 shorten and then lengthen. Numerous other hypotheses still less 

 probable have been published at various times. 



THE THERMO-DYNAMIC THEORY. The thermo-dynamic theory just 

 now seems perhaps more satisfactory than any other. By means of a 

 coil of platinum wire surrounding a short string of catgut kept warm in 

 a proper solution, Engelmann demonstrated that this form of proto- 

 plasm at least shortens when heat is applied to it (the heat was produced 

 by sending an electric current through the platinum wire). Rubber 

 behaves essentially in the same way. The curve made on a rotating 

 smoked drum by both of these substances under these conditions is 

 much like that traced by a contracting gastrocnemius of the frog (see 

 p. 473 of the Appendix). This experiment was at the basis of Engel- 

 mann's thermodynamic theory. His supposition, in fine, then, is that 

 metabolism (probably the katabolism) of carbohydrates causes a liber- 

 ation of heat in or about the myoids of muscle, and so causes them to 

 shorten. The main objections raised to this theory amount to an 

 assertion (as, for example, by Fick) that the heat-increase which actually 

 obtains in a contracting muscle is not sufficient to produce the effects 

 observed. In answering this, Engelmann suggests a rather far-reaching 

 principle, useful, perhaps, in more than this one place: the temperature 

 of some of the chemically acting individual particles in a muscle might 

 increase many degrees and yet not raise the temperature of the muscle- 

 mass (two-thirds water) more than a thousandth of a degree. At the 

 same time the heat rapidly produced by means of these relatively few 

 metabolizing particles might very well cause the muscle to contract.. In 

 general terms, that which takes place in an ultra-microscopic group of 

 molecules may be very different from what our relatively gross instru- 

 ments allow us to observe in an organ as a whole. 



On the basis of this rapid heating and cooling of minute metabolic 

 parts of a muscle the next supposition of the thermodynamic theory is 

 that this heating of the segments of the myoids or sarcostyles causes the 

 liquid of the isotropic (light-banded) segments of the sarcomere to be 



