256 PHYSIOLOGY OF MUSCLES AND NERVES. 



same irritants whicli act on the nerve are also able to 

 act on a muscle, and even on a muscle poisoned with 

 curare. We have, however, found slight differences, 

 and, if it were possible to show the existence of greater 

 differences, especially if irritants were found which act 

 on muscle-substance but not on nerve-sabstance, a new 

 point of departure would be gained for this theory of 

 independent irritability. Chemical irritants are beyond 

 all others capable of variation. From the endless num- 

 ber of chemical bodies we may choose such as irritate 

 the nerve or muscle in general, and we may try each of 

 these in every degree of concentration. If differences 

 between nerve-substance and muscle-substance really 

 exist, it is probable that we shall find them by these 

 means. Starting from these premisses, Kiihne experi- 

 mented on the condition of nerves and muscles ; and 

 he was so far successful that he discovered some dif- 

 ferences. 



In studying the character of nerves and muscles 

 relatively to chemical irritants, it is best to make a 

 cross-section, and to apply the substance which is to 

 be tested to this section. It is best to apply the test 

 to a thin parallel-fibred muscle, usually to the musculits 

 sartoriiis of the upper leg. It is suspended upside 

 down from a vice, which holds fast its lower pointed 

 tendon; and its upper end, which now hangs down- 

 ward, is then cut. The liquid which is to be tested is 

 then brought in contact with the cross-section thus 

 made, and care is taken to observe whether a pulsa- 

 tion takes place or not. The short, used portion having 

 then been cut off, the experiment can be repeated, 

 and so on till the whole length of the muscle has been 

 used. The nerve is treated similarly ; the sciatic nerve 



