ABNORMAL IRRITABILITY PRODUCED By SaLts 705 
traction I may mention hard rubber, glass, filter paper, var- 
nished and unvarnished wood, bone, muscle, all kinds of 
metals. Among the liquids tried were oil, glycerin, sugar 
solutions and several salt solutions. It is thus obvious that 
in a sodium-citrate solution two influences are united, first 
the effects of the citrate ion which causes a modification or 
an increase in the irritability of the nerve, and second, the 
liquid character of the solution. The latter is the direct 
cause for the contraction. 
Another point is of interest in this connection. The 
sodium-citrate or sodium-fluoride solution increases the elec- 
trical irritability of the nerve so that it can easily be stimu- 
lated by its own current of demarkation. This increase 
occurs regularly before the twitchings of the muscle begin. 
In my experiments on artificial parthenogenesis in Chee- 
topterus I found that there are two ways by which the 
unfertilized egg can be caused to develop —first, by certain 
ions (K, H), and second, by causing the egg to lose water. 
It follows from the facts of dissociation that a loss of water 
on the part of the egg must alter the proportion of ions in 
the egg. It thus becomes possible that the artificial par- 
thenogenesis produced by the loss of water is in reality an 
ion effect. In regard to the twitchings caused by putting 
the nerve into solution Mathews has shown that two cases 
must be distinguished —first, the effect of specific ions, and 
second, the effect of loss of water. Any solution whose 
osmotic pressure is high enough can cause contractions if 
the nerve be put into it. Is it not possible that the loss of 
water in the nerve acts in the same way as the citrate or 
fluoride ions? The limited solubility of CaSO, would make 
this possible. I tried whether a nerve after having been 
put into a 2n sugar solution long enough to cause muscular 
contractions would show the above-mentioned mechanical or 
contact-irritability. This was indeed the case. If such a 
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