STRUCTURE OF THE MEDUSZ. ys 
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 the 
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 ef 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 ihr 
Nervensystem untersucht” (Tiibingen, 1878). 
