PART II. 



THE MECHANICAL PROCESSES. 

 MUSCULAR CONTRACTION. 



MUSCLE consists of parallel fibres, each of which is a 

 tube containing contractile living substance. This living 

 substance is of two kinds, which differ in their optical 

 properties, and are arranged in layers alternating with 

 each other. In contraction their absolute and relative 

 volumes alter. So long as the tissue is living, the con- 

 tractile substance can be squeezed out as juice (muscle- 

 plasma), but after death it solidifies and exhibits a tendency 

 to split, transversely and longitudinally. Muscle is neutral 

 when living, acid after death. Muscle-plasma coagulates 

 spontaneously at all temperatures above that of freezing. 

 At 40 C. coagulation is instantaneous : the promptitude 

 with which it occurs is the less, the lower the temperature. 

 The coagulum is myosin (see p. 31). 



The chemical changes which constitute the life of muscle 

 manifest themselves in the production of CO 2 and H 2 O, 

 which are disengaged in the proportions in which they 

 result from the combustion of carbohydrates. When the 

 tissue is inactive, these are formed in very inconsiderable 

 quantities ; but in muscular activity, the rate of discharge 

 is increased in proportion to the work done. 



Living muscle is elastic, contractile and transparent. 

 As life ceases it stiffens, shortens, loses its contractility 

 and transparency, and the contents of its fasciculi become 

 solid. Death of muscle is promoted by defective blood 

 supply, high temperature or injury. It is slow and 



