348 CHEMICAL CHANGES OF LIVING MUSCLE. [BOOK I. 



bulk, as in the act of contraction. The lift of a muscle passing 

 into rigor is greater with a small load, but less with a heavy load, 

 than during a single contraction, and the absolute force is in the same 

 circumstances sometimes greater and sometimes less. No similar 

 comparisons have yet been made between rigid and tetanized muscles 1 . 



Rigid muscle is less extensile, as well as less elastic, than normal 

 resting muscle, thus differing from contracted muscle, which is more 

 extensile. It is, farther, distinguished from contracted muscle by its 

 peculiar doughiness and opacity. 



Rigor is associated with the evolution of heat post mortem 

 elevation of temperature. This is doubtless in part a mere conse- 

 quence of the physical changes of density, and the transformation 

 from the fluid to the solid state. But a physical explanation will not 

 account entirely for the phenomenon ; for no rise of temperature can 

 be detected during the quasi-rigor which is a simple coagulation 

 induced by acids or alcohol, and true rigor is unquestionably attended 

 by chemical changes 2 . 



The passage into rigor is further associated with a difference of 

 electric potential; dying muscle, like contracting muscle, is negative 

 to normal resting muscle 3 . 



Thus the last event in the life-history of muscle resembles a 

 common contraction very closely in the nature of its physical 

 phenomena. We shall find that they are alike also in their chemical 

 changes. 



SECT. 3. SPECIAL STUDY OF THE CHEMICAL CHANGES OF LIVING 



MUSCLE. 



It has been pointed out that the whole life of muscle consists 

 of two parallel series of transformations, of constitution and of 

 energy. The characters of one series, the transformations of energy, 

 have been rapidly sketched ; and it now remains to describe 

 in detail the changes of the other, or chemical series. It may at 

 once be stated that our knowledge of these two series is, and 

 must be, of very different extent. In the case of the physical trans- 

 formations w r e are able to study their course in time, to fix their 

 maximum and trace their decline. In the case of the chemical 

 series the steps are entirely hidden ; we can merely compare the 

 constitution of a muscle before and after, but not during, an act of 

 contraction. We cannot say whether the chemical changes run pari 



1 E. Walker, "Die absolute Kraft der Erstarrung." Pfliiger's Arch., Vol. iv. p. 186. 



2 Hermann, Handbuch der Physiol, Vol. i. Abth. i. p. 171. Schiffer, " Ueber die 

 Warmebildung erstarrender Muskeln." Arch. f. Anat. Physiol. u. wiss. Med. (Keichert 

 and du Bois-Keymond), 1868, p. 442. 



3 For a full account of the demarcation-current and its relation to the so-called 

 natural muscle-current of du Bois-Reymond, see Hermann's Handbuch, Vol. i. Abth. i. 

 p. 173 et seq. 



