RHYTHMICAL ContTRACTIONS IN MuscLE 537 
strong does not injure the dog, the conclusion cannot be 
drawn from this that a morphine solution is more harmless 
the greater its concentration, I do not doubt but that, 
when a ventricle which does not beat in a 0.7 per cent. NaCl 
solution containing 0.026 per cent. CaCl, is introduced in- 
to a 0.7 per cent. solution containing 0.04 per cent. CaCl,, 
and the quantity of the solution is the same in both cases, 
the ventricle will not beat in the latter caseeither. Whether 
a very dilute CaCl, solution, the concentration of which lies 
far below that of the serum (that is, far below 0.026 per cent.), 
is able to augment the stimulating effect of a NaCl solution 
is yet to be tested, and might easily be made to harmonize 
with what has been said above. 
14. Conclusions. 
a) There are certain ions—for example, Na, Cl, Li, F, 
Br, I, and others—which (in solutions having an osmotic 
pressure of 4.91 atmospheres) are capable of calling forth 
rhythmical contractions in muscles. These contractions are 
not brought about in that the given ions increase the irrita- 
bility, since, first, these contractions may continue even when 
the irritability has been diminished; and, secondly, since in 
solutions of non-electrolytes (for example, glycerin and 
sugar) of the same osmotic pressure these contractions do 
not occur even when the tissues have their normal irritability. 
It is to be believed rather that the entrance of the ions 
mentioned above into definite compounds in the muscle is 
the cause of these contractions. 
b) There are ions which inhibit the liberation of rhyth- 
mical contractions of the normal muscle; for example, Ca, K, 
Mg, Be, Sr, Co, and Mn. The inhibiting effect of Ca, K, 
and possibly also the other ions, does not rest upon the fact 
that they reduce the irritability of the muscle; for through 
the addition of only a small amount of CaCl, to a physi- 
ological salt solution the contractions are prevented, while 
Digitized by Microsoft® 
