CHAPTEK IX 



CHANGS IN FORM IN A MUSCLE WHEN IT CONTRACTS 



THOUGH it has been known since the time of Erasistratus (B.C. 304) 

 that a muscle becomes thicker and shorter when it contracts, it was 

 not until the invention of the graphic method by Ludwig and Helm- 

 holtz, about sixty years ago, that we possessed any accurate knowledge 

 of this change. The main fact just stated may be seen by simply 

 looking at a contracting muscle, such as the biceps of one's own arm ; 

 but more elaborate apparatus is necessary for studying the various 

 phases in contraction and the different kinds of contraction that may 

 occur. 



These may be readily demonstrated on the ordinary muscle-nerve 

 preparation (gastrocnemius and sciatic nerve) from a frog. By the 

 graphic method, one means that the movement is recorded by a writ- 

 ing. We shall find that the same method is applied to the heart's 

 movements, respiratory movements, blood pressure, and many other 

 important problems in physiology. The special branch of the graphic 

 method we have now to study is called myography ; the instrument 

 for writing is called a myograph ; the writing itself is called a myogram. 

 Put briefly, a myograph consists of a writing point at the end of a 

 lever attached to the muscle, and a writing surface which travels at a 

 uniform rate, on which the writing point inscribes its movement. 



The first thing, however, that is wanted is something to stimulate 

 the muscle and make it contract ; the stimulus is usually applied to 

 the nerve, and the form of stimulus most frequently employed is 

 electrical. 



The galvanic battery in most common use is the Daniell cell. It 

 consists of a well-amalgamated zinc rod immersed in a cylinder of 

 porous earthenware containing 10 per cent, sulphuric acid; this is 

 contained within a copper vessel (represented as transparent for 

 diagrammatic purposes in fig. 105) filled with saturated solution of 

 copper sulphate. Each metal has a binding screw attached to it, to 

 which wires can be fastened. The zinc rod is called the positive 

 element, the copper the negative element. The distal ends of the wires 



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