ALTERATION IN FORM DURING CONTRACTION. 45 



raises the question whether the muscle in contracting 

 has undergone no cliange in the amount of space oc- 

 cupied by it, or if its mass has become more dense. 

 It is not easy to determine this accurately, for the 

 alteration in the volume of the muscle can only be 

 v^er}'^ slight. Experiments which have been made by 

 P. Erman, E. Weber, and others, agree in showing 

 that a very slight diminution in the muscle does cer- 

 tainly take place. 



Remembering, however, that muscle consists of a 

 moist substance, and that about three-fourths of its 

 whole weight is water, even this slight decrease in 

 volume must be the result of very considerable pressure 

 — for fluids are extremely difficult of compression — un- 

 less possibly a portion of the water is expressed through 

 the pores of the sarcolemma pouch. 



^lore important than this structural change of the 

 whole muscle is the change of form which each separate 

 muscle-fibre undergoes. This may be observed under 

 the microscope in thin and flat muscles, when it will 

 be found that each muscle-fibre also becomes both 

 shorter and thicker. On placing a muscle on a glass 

 plate under the microscope, in order to observe this, 

 the muscle, when the irritant ceases to act, is seen to 

 remain apparently in its shortened form. But the 

 separate muscle-fibres resume their former length as 

 soon as the irritant ceases, and they therefore lie in a 

 zigzag position until they are straightened by some 

 external force. I merely mention this here, because 

 the phenomenon is of historic interest. Prevost and 

 Dumas, who were the first to examine this condition, 

 believed that the contraction of the whole muscle was 

 due to this zigzag bending of the muscle-fibres. With 



