CHEMICAL AND MECHANICAL ENERGY. 393 



following phenomena, many of which have been indicated by Schiff or 

 his pupils, tend to support this view: 1 — (1) Whenever rigor comes on 

 very gradually, the muscles continue for some time to respond to appro- 

 priate stimuli (interruption of a battery current led through the muscle, 

 or tapping of the surface). If the stimulated parts are afterwards com- 

 pared with other parts, they are found to be rigid and unexcitable. This 

 can be observed both in the frog and in mammals. (2) If a muscle in the 

 transition state above referred to, is observed with the aid of the electro- 

 meter, the meniscus is seen to oscillate in such a way as to indicate the 

 existence of irregular action currents. In some muscles, when going 

 into rigor, irregular contractions are observable. This is chiefly 

 seen in mammalian muscles (Brown - Sequard), although it is also 

 noticeable in some amphibians, e.g. in toads and, to a less extent, in 

 Rana temporaria. In R. esculenta the passing into rigor is almost 

 always a continuous process. (3) Schiff finds it impossible to determine 

 when the initial shortening of muscles deprived of their supply of 

 arterial blood by ligature, as in Stenson's experiment, ceases to be con- 

 traction and becomes rigor. The distinction between them is so gradual, 

 that the muscles can at first be brought back to their normal state by 

 restoring the circulation ; later, this becomes more and more difficult. 

 (4) In a frog poisoned by strychnine after one sciatic nerve has 

 been divided, the spasm of strychnine in the poisoned limb passes 

 so immediately into that of rigor, that it is difficult to distinguish 

 them. Here Schiff attributes the initial contraction to the chemical 

 stimulus (lactic acid ?) brought into existence by the previous spasm. 

 For, according to his pupil, C. Schipiloff, the first effect of the 

 circulation of salt solution containing - l per cent, of sarcolactic 

 acid, is to produce spasm. The muscles, however, retain their trans- 

 lucency, and can be brought back to the normal by substituting 

 alkaline for acid salt solution. If this is not done, the spasm passes 

 into rigor. 



The general result of the preceding considerations relating to the 

 nature of rigor mortis is — (1) That rigor is a mixed process, of which 

 the first stage is spasmodic, the second coagulatory ; (2) that although 

 the spasmodic phenomena for the most part precede the coagulatory, 

 the two may present themselves simultaneously ; (3) that although 

 there is no sufficient evidence that the presence of free lactic acid is the 

 cause of the dying contraction of muscle, acid reaction is its earliest con- 

 comitant ; (4) that post-mortem spasm is of similar nature to those 

 continuous contractions which, although they occur during life, are 

 characterised by (a) extreme slowness or even absence of propagation, (b) 

 slowness of development, and (c) by the fact that they are relatively 

 more readily evoked by stimuli of a certain duration than by instan- 

 taneous stimuli. 



Nature of the Process by which Chemical Energy is Transformed 

 into Mechanical Energy in Muscular Contraction. 



The mechanical potential energy which suddenly comes into exist- 

 ence when a muscle is excited, whether this is allowed to manifest itself 

 in lifting a weight, or is compelled to appear exclusively as tension, has its 

 ultimate source in the chemical potential energy of certain constituents 



1 "Beitr. z. Physiol.," 1894, S. 97-124. 



