33 
much of the muscle-proteid was taken up by the anions of the 
solution. Of course, the wave of positivity thus produced, on 
issuing from the region immersed, would be converted into a 
wave of negativity again, owing to the anions displacing 
kations ; but it would probably be reduced owing to some of 
the anions combining directly with kations. This idea re- 
ceives support from the fact that nerves which have been im- 
mersed for a long time in salt solution, and are repeatedly 
stimulated, give a wave of positivity.'^ Still more suggestive 
is the fact that the excitatory state is often diminished when 
passing through a portion of nerve treated with NaCl — -abso- 
lutely with a 6"1 per cent. Nal solution — though excita- 
bility is still present.! Thus the wave of negativity is, in the 
second instance, suppressed, as we have said it may be, 
though a wave may be started from the point affected by 
direct action of the current. The reason why the wave is so 
absolutely suppressed in the case of Nal is probably the high 
stimulation efficiency of Nal causing a great predominance 
of anions ; as we shall see, the number of kations in a normal 
wave of negativity in medullated nerve is small. 
It will be obvious that there is a difficulty in proving this 
point in nerve, because the wave of positivity in the affected 
region is converted into a wave of negativity directly it 
emerges. But our previous investigations into the contrac- 
tion of muscle show that a wave of positivity cannot cause a 
contraction until it be converted into a wave of negativity, 
because a wave of positivity would only diminish, not increase, 
the P.D. between the hyaloplasm and spongioplasm, and, 
therefore, the surface tension at their contact surface would 
not be diminished, and no contraction would ensue : hence, a 
portion of a muscle which has been treated with a solution 
which has a sufficiently great negative stimulation efficiency 
ought to act as a motor nerve to the rest. 
This can be very easily demonstrated in the intestine of a 
fly. In insects the walls of the intestine contain 'striated 
(uninuclear) muscle cells, which by contraction set up the nor- 
mal peristaltic movements of the digestive tract.'' i The 
species I used for experiments was Callophora villosa, Desv., 
which is the Australian representative of the English blue- 
bottle. If the last posterior segment of one of these flies is 
torn away with forceps, the end of the intestine is usually 
left hanging from it, and, if the operation be performed care- 
fully, nearly half an inch of intestine can sometimes be 
* Gotcli : Schafer's Textbook of Physiology, vol. ii.. page 538. 
t Got eh : Schafer's Textbook of Physiology-, vol. ii.. page 490. 
t Bi'e<:lermann : Electro -<jh\riology : Trans, by F. A. Welby. 
vol. i.. page 164. 

