496 EDGAR J. ALLEN. 
and in its normal condition. It will be seen that the terminal 
swellings are of exactly the same nature as those found on the 
nerve-endings. (Compare figs. 6 and 12.) Hence this is 
clearly a form which fine branches of living protoplasm are 
capable of assuming. Under these circumstances, in the 
absence of direct observation to the contrary, it seems more 
natural to suppose that the terminal swellings on the nerve- 
endings also represent the normal condition. 
In this connection the recent observations of Ballowitz! 
upon the chromatophores of fishes are of interest, confirming 
the fact that the retractile pigmented protoplasm represents 
only a portion of the protoplasm of the cell process, the process 
itself remaining always fully expanded. Should this view be 
correct, the question naturally arises, does the portion of a 
branching nerve-fibre which takes up methylene blue represent 
the whole protoplasm, or only that portion which corresponds 
to the pigmented protoplasm of the chromatophore ? 
Both the phenomena of beading and the formation of end- 
swellings appear to be due to a simple physical cause, namely 
the difference of surface tension between two fluids. A fluid 
cylinder surrounded by some other fluid of different surface 
tension is in a condition of unstable equilibrium, and tends to 
break up into spherical drops. A stream of water issuing 
through a circular orifice and allowed to fall for some distance, 
goes through much the same series of changes as those which 
have been described for a beaded nerve-fibre, until it finally 
breaks up into spherical drops. I have been able to produce 
fibres which have almost exactly the same size and assume the 
same variety of shapes as beaded nerve-fibres in a very simple 
way. A thick syrup of gum and sugar is made, and a drop of 
this is placed in the centre of a glass slide, which has been 
covered with a layer of paraffin oil. If fine threads are drawn 
from the syrup across the oiled surface of the glass, with the 
point of a knife or a rough needle, on examining under the 
1 Ballowitz, ‘Die Nervenendigungen der Pigmentzellen,’”’ ‘ Zeitschr. 
wiss. Zool.,’ 56, 1893; “ Ueber die Bewegungserscheinungen der Pigment- 
zellen,” ‘ Biol. Centr, bl.,’ xiii, 1893, p. 625, 
