STRUCTURE OF THE MEDUSA. 28 



Professor Eimer.* He began, like myself, by what 

 in the next chapter I call the " fundamental obser- 

 vation " on the effects of excising the nerve- 

 centres, and from this basis he worked both at the 

 physiology and the morphology of the neuro- 

 muscular tissues. In point of time, I was the first 

 to make the fundamental observation, and he was 

 the first to publish it. The sundry features in which 

 our subsequent investigations agreed, and those in 

 which they differed, I shall mention throughout the 

 course of the following pages. 



I shall now conclude this chapter by giving a 

 brief account of those general principles of tlie 

 physiology of nerve and muscle with which it is 

 necessary to be fully acquainted, in order to under- 

 stand the course of the following experiments. 



Nerve-tissue, then, universally consists of two 

 elementary structures, viz. very minute nerve-cells 

 and very minute nerve-fibres. The fibres proceed 

 to and from the cells, so in some cases serving to 

 unite the cells with one another, and in other cases 

 with distant parts of the animal body. Nerve-cells 

 are usually found collected together in aggregates, 

 which are called nerve-centres or ganglia, to and 

 from which large bundles cf nerve-fibres come 

 and go. 



To explain the function of nerve- tissue, it is 

 necessary to begin by explaining what physiologists 

 mean by the term " excitability." Suppose that a 



* " Die Medusen physiologisch und morphologisch auf il.r 

 NerveuBvstem untersucht " (Tixbingen, 1878). 



