Causation of Vital Movement. 



435 



Fig-. 1. Fig. 2. 



sartorius suspended in ammonia vapour, contracting powerfully, while 

 a nerve entirely submerged in liquid ammonia appears wholly 

 unstimulated, for it does not rouse the thigh muscles from their 

 repose. (Experiment shown.) 



Conversely, we see a thigh whose nerve dips into glycerine in 

 maximal contraction, and on the other hand, a muscle in contact at its 

 excitable end with the same glycerine remains at rest, yet it twitches 

 if I dip it in up to its nerve-bearing tracts (11). 



These are old experiments (12), and it is admitted they have over- 

 thrown the earlier opinion. But they have not been deemed sufficient to 

 prove muscular irritability, because the ultimate endings of the nerves 

 might have an irritability other than that of their stems. This is the 

 only objection still raised. One could wish no other were con- 

 ceivable, for this one admits of refutation. 



To this end permit me to go a little into detail concerning nerves. 

 Nerves are processes of nerve-cells composed of fibrils of immeasur- 

 able fineness, which in the so-called axis cylinder of the medullated 

 nerves are united by a stroma inside a very fine membrane called the 

 axolemma. In proportion to the microscopic dimensions of the 

 ganglion cells of which the separate nerve-fibres form a part, these 

 latter are for the most part enormously long, many as long as our 

 arms and legs, and that is one of the reasons why the perception of 

 the unicellular nature of the nerves made way but slowly. In fact it 

 was not easy to accustom oneself amid the microscopic swarm of cells, 

 to find single ones so grown in length that they could be wound 

 about us like a cocoon thread. As it is the task and function of the 

 motor nerves to lead towards the periphery the impulses sent out by 

 their ganglion cells in the spinal cord, their activity always admits of 

 ready perception through the muscular twitching. Even when the 



