106 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Fig. 40.— a, Curve of extensibility 

 and elasticity of a rubber band ; b, curve 

 of extensibility and elasticity of a sar- 

 torius muscle of a frog. The weights 

 employed were 10 grams each. The 

 same length of time was allowed to 

 pass between the adding and subtract- 

 ing of tlie weights. 



conditions. Under these circumstances it is found that if a number of equal 

 weights be added t<> a suspended muscle, one after the other, the extension pro- 

 duced is not, like that of an inorganic body 

 such as steel spring, proportional to the weight, 

 but each weight stretches the muscle less than 

 the preceding. If the weights be removed 

 in succession, an elastic recovery is observed, 

 which, although considerable, is incomplete. 

 If the change in the length be recorded by 

 a lever attached to the muscle, the surface 

 being moved along just the same amount after 

 each weight is added or removed, a curve is 

 obtained such as is shown in Fig. 40, b. 

 Above this is a record taken in a similar way 

 from a piece of rubber (a). The rubber resem- 

 bles a steel spring in that equal weights stretch 

 it to like amounts, but the elastic recovery, 

 though more complete than that of the muscle, 

 is imperfect. 



In such an experiment it is found that the 

 full eifect of adding the weights, or removing 

 them from the muscle, does not occur immedi- 

 ately, but when a weight is added there is a 

 gradual yielding to the stretching force, and, on the removal of a weight, a 

 gradual recovery of form under the influence of the elasticity. This slow 

 after-action makes it difficult to say just what is to be considered the proper 

 curve of elasticity of muscle, especially as the physiological condition of the 

 muscle is always changing. The elasticity of muscles is dependent on normal 

 physiological conditions, and is altered by death, or by anything which causes 

 a change in the normal constitution of the muscles, as the cutting off of the 

 blood-supply. The dead muscle is less extensible and less elastic than the 

 normal living muscle. Heating, within limits, increases, and cooling decreases 

 the elasticity, possibly by altering the mobility of the semifluid materials of 

 the muscle, and hence changing the internal friction. 1 Contraction is accom- 

 panied by increased extensibility, i. e. lessened elasticity — and the changes 

 caused by fatigue lessen the elasticity. It is interesting to note in this con- 

 nection that the elasticity is decreased by weak acid solutions and increased 

 by weak alkaline solutions (Brunton and Cash). 2 



The elasticity of a muscle within the body is generally considered to be 

 more perfect than that of the isolated muscle, but even here one can observe 

 the after-stretching described by Weber and the contraction remainder 

 described by Hermann. Mosso 3 suggests the following experiment on man : 



1 Blix : Skandinavisches ArchivJ'ur Physiologie, 1893, iv. S. 392. 



2 Philosophical Transactions, 1884, p. 197. 



s Mosso : Archives ilaliennes de Biologie, 1895, xxv. p. 27. 



