554 A MANUAL OF PHYSIOLOGY 



at the anode ; and that the make is stronger than the break 

 contraction. This is true both for muscle and nerve, but it 

 is most directly and simply demonstrated on muscle. A 

 long parallel-fibred curarized muscle is supported about its 

 middle; the two ends, which hang down, are connected 

 with levers writing on a revolving drum, and a current is 

 sent longitudinally through the muscle. It is not difficult 

 to see from the tracings that at make the lever attached to 

 the cathodic end moves first, and that the other lever only 

 moves when the contraction started at the cathode has had 

 time to reach it in its progress along the muscle. Similarly, 

 at break the lever connected with the anodic end moves first. 

 The Muscular Contraction. When a muscle contracts, its 

 two points of attachment, or, if it be isolated, its two ends, 

 come nearer to each other ; and in exact proportion to this 

 shortening is the increase in the average cross-section. The 

 contraction is essentially a change of form, not a change of 

 volume. The most delicate observations fail to detect the 

 smallest alteration in bulk (Ewald). Living fibres kept 

 contracted by successive stimuli can be examined under the 

 microscope ; or fibres may be ' fixed ' by reagents like osmic 

 acid, and sometimes a very good opportunity of studying 

 the microscopic changes in contraction is given by a group 

 of fibres in which the ' fixing ' reagent has caught a wave 

 of contraction, and, so to speak, pinned it down. It is then 

 seen that the process of contraction in the fibre is a miniature 

 of that in the anatomical muscle. The individual fibres 

 shorten and thicken, and the sum-total of this shortening 

 and thickening is the muscular contraction which we see 

 with the naked eye. The phenomena of the muscular con- 

 traction may be classified thus : (i) Optical, (2) Mechanical, 

 (3) Thermal, (4) Chemical, (5) Sonorous, (6) Electrical. 

 (5) will be treated under * Voluntary Contraction '; (6) in 

 Chapter XL 



(i) Optical Phenomena Microscopic Structure of Striped 

 Muscle. The structure of striped muscle has long been the enigma 

 of histology ; and the labours of many distinguished men have not 

 sufficed to make it clear. On the contrary, as investigations have 

 multiplied, new theories, new interpretations of what is to be seen, 

 have multiplied in proportion, and a resolute brevity has become the 



