MUSCLE 225 



beyond the point at which it has ceased. This method of 

 recordino: the force of contraction is sometimes called the 

 isometric method, in distinction to the isotonic method of 

 letting the muscle act upon a light lever. 



Muscle may start contracting isometrically, overcoming 

 the inertia of the weight, and then proceed in isotonic 

 contraction while lifting the weight ; or the converse con- 

 dition may occur. 



In clinical medicine the dynamometer is used for 

 measuring the force of muscular contraction. This has 

 generally the form of an oval steel spring which is com- 

 pressed by the hand. The degree of compression is indicated 

 on a dial (Practical Physiology). 



The contraction of the unexposed muscles in the body of the 

 mammal may be studied by recording their thickening by 

 means of Marey's muscle forceps. These consist of a tam- 

 bour, placed between one pair of the limbs of forceps hinged 

 in the centre. This is pressed upon by the contraction 

 of a muscle or group of muscles held between the opposite 

 limbs. The pressure is transmitted by a tube to another 

 tambour which carries a recording lever (Practical Phy- 

 siology). 



It may also be investigated by fixing a limb and attaching 

 the tendons of the muscles to be studied to levers. This 

 method has been used by Sherrington in his work upon reflex 

 action. 



The Factors modifying' Contraction. — 1. Kind of Fibre. — 



In skeletal muscles, the j:>rt^e fibres contract more rapidly and 

 completely than the red fibres, which contain more sarco- 

 plasm and nuclei. The peculiarities of the contraction of 

 visceral muscles have been already considered. 



2. Species of Animal. — In vertebrates, the contraction of 

 the muscles of warm-blooded animals is more rapid than the 

 contraction in cold-blooded animals, in the rabbit about 

 07 sec. The most rapidly contracting muscles are met 

 with in msects. 



•3. State of the Muscle. — (1) Continued Exercise.- —If a 

 15 



