the influence of electrolytes upon the surface tension, taken 
in conjunction with the ion-proteid theory, does not appear 
to have been worked out. Loeb"^ alludes to his conviction 
that the electrical energy of the ions in an electrolyte is trans- 
formed into surface energy at the surface of an organism sus- 
pended in it ; but, as far as I have read his writings, he does 
not explain how this is accomplished, nor does he apply the 
idea. Mannt suggests that the electrical charge on colloid 
particles in solution may be due to the formation of definite 
compounds between the colloid and one or other of the ions 
in the solution, an hypothesis of which I make frequent use 
throughout this paper. Strong' | has developed a theory of 
the nervous impulse, which regards it as due to free ions in 
the nerve, but as he does not adopt the ion-proteid theory he 
is forced to make assumptions — such as the semi-permeability 
of proteid to certain ions — which render his theory of very 
limited application. 
I had already written the greater part of this paper when 
the American Journal of Physiology for March, 1904, arrived, 
containing Lillie's paper § on the toxic and anti-toxic effects 
of certain salts. In ffhis he suggests that certain phenomena 
of movement in unicellular organisms may be due to surface 
tension alterations, due to ions in the medium, and he uses 
the analogy of the capillary electrometer ; but, as far as con- 
tractility is concerned he does not appear to have applied the 
idea or to do more than throw it out as a suggestion ; that is, 
so far as my acquaintance with his writings goes. Still more 
recently, Matthews' paper on the nature of chemical and 
electrical stimulation has appeared. In this he does not pro- 
fess to give an explanation of the physico-chemical mechan- 
isms of protoplasmic movement and excitation. Nevertheless, 
he concludes, as I do, "that the chemical composition of the 
ion is of little importance compared with the importance of 
its electrical condition." IT He also considers that electrical 
stimulation "is due simply to the accumulation of negative 
""' Jacques Loeb : American Journal of Physiology, 1902, 
ii., page 411. 
t Gustav Maam : Physiologica.] Histology : Methods «ud 
TJLeoiT, 1902, pages 45 and 46. 
X W. M. Strong : A Physical Theory of Nerve. Journal of 
Physiology, 1900, vol. xxv., page 427, 
§ Ra/lph S. Lillie : The Relation of Ions to Ciliary Move- 
ment. American Journal of Physiology, March, 1904. 
II The Nature of Chemical and Electrical Stimulation : 
1. The physiological action of an ion depends upon its elec- 
trical state and its electrical stability. A. P. Matthews : American 
Journal of Physiology, August, 1904. 
II American Journal of Physiology, vol. xi., No. 5, page 456. 
