846 ACTION" or long .4XD 



principle, it must follow that the shorter the fibre is 

 the sooner must it be \Yholly brought into action, and 

 the sooner also must its individual effort be over. 

 All muscular action (as the reader must of course be 

 aware) consists in a contracting or shortening of the 

 fibres, and a proportional increase in thickness. How 

 the shortening takes place is a part of the subject 

 upon which it would not be very wise to offer any 

 conjecture, as it is one upon which we possess no 

 knowledge ; but the action itself can be observed, and 

 we may rationally conclude that the times in which 

 equal degrees of excitement are communicated to 

 muscles are in proportion to the lengths of their 

 fibres : that one-half of the length will be brought into 

 action in half the time, and so of all other proportions. 

 This will hold true, whatever may be the absolute 

 length of the time, even though it should be, as it no 

 doubt is in the case of very minute muscles, too 

 short for our being able to measure, or in any way 

 estimate its length in terms of any other motion. But 

 as the shorter muscle must act in the shortest time, so 

 the action of the longer one must be greater, if the 

 requisite time is allowed it — it must contract more, or 

 be capable of moving the same w^eight over a greater 

 space. 



From the indeterminate quantities, which we have 

 no means of separating, or even of expressing, that, 

 as already noticed, enter into the very complex ope- 

 ration of muscular action, what has been now stated 

 can be regarded only as a glimmer in the dark, yet 

 it is far from being without its use, especially in the 

 comparison of structures so varied in their actions, 

 yet all formed on the same general principle, as the 

 wings of birds. 



A short muscle will, from what has been said, per- 



