- 82 TETANUS. [BOOK i. 



If the lever, instead of being fastened to the tendon of a muscle 

 hung vertically, be laid across the belly of a muscle placed in a 

 horizontal position and the muscle be thrown into tetanus by a 

 repetition of induction-shocks, it- will be seen that each shortening 

 of the muscle is accompanied by a corresponding thickening, and 

 that the total shortening of the tetanus is accompanied by a cor- 

 responding total thickening. And indeed in tetanus we can observe 

 more easily than in a single contraction that the muscle in contract- 

 ing changes in form only, not in bulk. If a living muscle or group 

 of muscles be placed in a glass jar or chamber, the closed top of 

 which is prolonged into a narrow glass tube, and the chamber be 

 filled with water (or preferably with a solution of sodium chloride, 

 '6 p. c. in strength, usually called "normal saline solution," which is 

 less injurious to the tissue than simple water) until the water rises 

 into the narrow tube, it is obvious that any change in the bulk of 

 the muscle will be easily shewn by a rising or falling of the 

 column of fluid in the narrow tube. It is found that when the 

 muscle is made to contract, even in the most forcible manner, 

 the change of level in the height of the column which can be 

 observed is practically insignificant : there appears to be a fall in- 

 dicating a diminution of bulk to the extent of about one ten-thou- 

 sandth of the total bulk of the muscle. So that we may fairly say 

 that in a tetanus, and hence in a simple contraction, the lessening 

 of the length of the muscle causes a corresponding increase in the 

 other directions : the substance of the muscle is displaced not 

 diminished. 



50. So far we have spoken simply of an induction-shock or of 

 induction-shocks without any reference to their strength, and of a 

 living or irritable muscle without any reference to the degree or 

 extent of its irritability. But induction-shocks may vary in 

 strength, and the irritability of the muscle may vary. 



If we slide the secondary coil a long way from the primary coil, 

 and thus make use of extremely feeble induction-shocks, we shall 

 probably find that these shocks, applied even to a quite fresh muscle- 

 nerve preparation, produce no contraction. If we then gradually 

 slide the secondary coil nearer and nearer the primary coil, and 

 keep on trying the effects of the shocks, we shall find that after a 

 while, in a certain position of the coils, a very feeble contraction 

 makes its appearance. As the secondary coil comes still nearer to 

 the primary coil the contractions grow greater and greater. After a 

 while however, and that indeed in ordinary circumstances very 

 speedily, increasing the strength of the shock no longer increases the 

 height of the contraction; the maximum contraction of which the 

 muscle is capable with such shocks however strong has been reached. 



If we use a tetanizing or interrupted current we shall obtain 

 the same general results ; we may, according to the strength of the 

 current, get no contraction at all, or contractions of various extent 

 up to a maximum, which cannot be exceeded. Under favourable 



