CHAP, ii.] THE CONTRACTILE TISSUES. 39 



poison ; and yet it has lost none of its power over the muscle. On 

 the other hand, if the muscle be allowed to remain in the body, and 

 so be exposed to the action of the poison, but the nerve be divided 

 high up and the part connected with the muscle gently lifted up 

 before the urari is introduced into the system, so that no blood 

 flows to it and so that it is protected from the influence of the 

 poison, stimulation of the nerve will be found to produce no con- 

 tractions in the muscle, though stimuli applied directly to the 

 muscle at once cause it to contract. From these facts it is clear 

 that urari poisons the ends of the nerve within the muscle long 

 before it affects the trunk, and it is exceedingly probable that it 

 is the very extreme ends of the nerves (possibly the end-plates, for 

 urari poisoning, at least when profound, causes a slight but yet 

 distinctly recognisable effect in the microscopic appearance of these 

 structures) which are affected. The phenomena of urari poisoning 

 therefore go far to prove that muscles are capable of being made 

 to contract by stimuli applied directly to the muscular fibres them- 

 selves ; and there are other facts which support this view. 



This question of 'independent muscular irritability' was once thought 

 to be of importance. In old times, the swelling of a muscle during con- 

 traction was held to be caused by the animal spirits descending into it 

 along the nerves; and when the doctrine of 'spirits' was given up, it 

 was still taught that the vital activity of the muscle was something 

 bestowed upon it by the action of the nerve, and not properly belonging 

 to itself. We owe to Haller the establishment of the truth, that the 

 contraction of a muscle is a manifestation of the muscle's own energy, 

 excited it may be by nervous action, but not caused by it. Haller spoke 

 of the muscle as possessing a vis insita, while he called the nervous 

 action, which excites contraction, the vis nervosa. He used the word 

 irritability as almost synonymous with contractility, a meaning which is 

 still adopted by many authors. In this work we have used it in the 

 wider sense, first employed by Glisson, which includes other manifesta- 

 tions of energy than the change of form which constitutes a contraction. 



The Phenomena of a simple Muscular Contraction. 



If the far end of the nerve of a muscle-nerve preparation 1 , 

 Figs. 1 and 2, be laid on the electrodes of an induction-machine 2 , 



1 By this is meant a muscle dissected out with some length of nerve attached to it, 

 both being in a living condition, i.e. still irritable. The muscle generally used is the 

 gastrocnemius of the frog, the attachment to the femur and a portion of the tendo 

 Achillis, together with a considerable length of the sciatic nerve, being carefully 

 preserved. 



2 It may perhaps be worth while to remind the reader of the following facts. 



In a galvanic battery, the substance (plate of zinc for instance) which is acted 

 upon and used up by the liquid is called the positive element, and the sub- 

 stance which is not so acted upon and used up (plate &c. of copper, platinum, or 

 carbon, &c.) is called the negative element. A galvanic action is set up when the 

 positive (zinc) and the negative (copper) elements are connected outside the battery 



