46 PRACTICAL PHYSIOLOGY 



branches upwards and downwards ; as a matter of 

 fact each nerve fibre divides into two branches, one 

 for the upper and the other for the lower part of 

 the muscle. The middle part of the muscle can be 

 entirely cut away without injuring these nerves, 

 and the two parts of the muscle will then only be 

 united by the forked nerves. 



If the ends of the nerves in either of the pieces 

 of the muscle are stimulated, whether electrically, 

 chemically (salt), or mechanically (by snipping with 

 scissors), both pieces contract. 



A similar experiment can be made with the sar- 

 torius, the nerve fibres of which branch as they pass 

 into the upper end of the muscle, so that if this end 

 is split down the middle, and the nerve fibres in 

 either half are stimulated, the other half of the split 

 part contracts. It will be remembered, however, 

 that there are no nerve fibres at the very end of 

 this muscle, so that to get the desired result i.e., 

 contraction of both halves the muscle must be 

 stimulated a short distance from this end. 



Effect of CO 2 on conduction in nerve. Take 

 a nerve-muscle preparation and lay the nerve across 

 and partly imbedded in a ring of soft modelling 

 clay placed upon a glass slide, to which a tube is 

 cemented so that a current of CO 2 can be conducted 

 over the nerve. The ring is covered by a cover 

 glass, and the end of the nerve projects beyond 

 it and rests upon a pair of electrodes (Fig. 30). 



Find the minimal stimulus which will produce 

 contraction of the muscle; then pass a current of 

 CO 2 over the intervening nerve, and determine the 



