128 Papers from the Marine Biological Laboratory at Tortugas. 
pulsation-wave is decreased both in rate and amplitude as it passes through 
B, but this is effected by each of these elements in its own peculiar manner. 
For example, magnesium soon renders the muscles incapable of contraction, 
but only later does it exert an inhibiting effect upon the nerves. Calcium, 
on the contrary, chiefly affects the nerves, and stops pulsation very sud- 
denly. At first the wave extends throughout the length of the strip immersed 
in the sea-water containing an excess of calcium, but soon it can penetrate 
ee eee ee 
Fic. 11.—Test for nervous or muscular nature of effects of various 
salts of sea-water. 
only part way through the calcium-affected portion of the strip, and the 
distance it can travel steadily decreases as time goes on until it is checked 
almost immediately after entering B from A. This gradual dying-out of 
the pulsation-stimulus is well seen in a strip immersed in 100 volumes of 
sea-water to which 40 volumes of a 5¢m solution of CaCl, has been added. 
In this solution the tissue ceases to transmit the pulsation long before tetanus 
is produced, but a stronger solution of calcium quickly produces tetanus. 
This calcium-tetanus is purely muscular, and is not transmitted to portions 
of the strip other than those immersed in the calcium solution itself. 
A similar experiment with an excess of potassium shows that the first 
effect of this salt is to stimulate pulsation, but its final effect is both inhibi- 
tory and toxic. Its toxie influence is prevented by calcium, and its effect 
in sea-water is simply to aid in the restraining of the stimulus due to sodium. 
We can prove that of the depressants to pulsation in sea-water, the most 
powerful inhibitor is magnesium, while calcium is moderately and potassium 
only weakly depressant. This is shown (fig. 12) when we take a long strip of 
subumbrella tissue having a single sense-organ (s) in the middle of its length, 
and stretch the strip across five shallow glass dishes (A—-E). If, then, we 
place natural sea-water in the middle dish C, and also in the two end-dishes 
A and E, we will be in a position to test the relative inhibiting powers of 
any two solutions placed in dishes B and D, respectively. In this manner 
we can show that a solution containing the amounts and proportions of 
NaCl-++ Mg of the sea-water is a more powerful inhibitor, and stops the 
pulsation-stimulus sooner than solutions of Na+ K, or Na+ Ca. More- 
over, a solution of NaCl-+ CaCl, stops pulsation sooner than a solution of 
NaCl -+ KCl, the amounts and proportions being in all cases those found 
in sea-water. 
