Tuer PHYSIOLOGICAL EFFEoTS oF Ions 453 
I undertook the determination of the physiological effects 
of the ions of a series of electrolytes on frog’s muscle. It 
seemed essential to my mind, however, to choose such reac- 
tions as are capable of exact quantitative determination. As 
such reactions I chose first of all the amount of water ab- 
sorbed by a muscle under the influence of certain electrolytes ; 
for I had found that the gastrocnemius muscle of the frog, 
which has, as is well known, usually about the osmotic pres- 
sure of a 0.7 per cent. NaCl solution, increases considerably 
in weight upon the addition of a trace of an acid or an alkali 
to this sodium-chloride solution. This increase in weight is 
chiefly due, no doubt, to the absorption of water. The second 
reaction which I chose was the influence of the electrolyte 
on the threshold of stimulation. Asa source of stimulation 
I used induction shocks, and as the measure of the threshold 
of stimulation, the greatest distance at which the secondary 
coil could be moved away from the primary and just appre- 
ciable contractions still take place. I attach less value to the 
latter method, because it seems to me that the irritability of 
the individual muscle fibers does not vanish at the same 
moment. When the electrodes are placed at one point, no 
effect may be appreciable; when they are moved, however, 
a slight twitching of individual fibers may yet be brought 
about. This method can, therefore, not be considered as 
accurate as the first method. 
II. EXPERIMENTS WITH ACIDS 
1. The normal solutions used in these experiments were 
made with the greatest care by Dr. Bernhard, assistant in 
the chemical laboratory. Solutions of the acids and alkalies 
were made which were one-tenth normal with reference to 
the H and OH contained in them. The HCl solution, for 
example, contained 1 gram-molecule (1 mol.) HCI in 10 liters 
of water; the H,SO, solution, only 4 mol. H,SO, in 10 
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