574 STUDIES IN GENERAL PHYSIOLOGY 
of rhythmical contractions. In this case the addition of Ca 
ions to a pure NaCl solution will produce rhythmical activity. 
In a former paper I have shown that skeletal muscle can be 
caused to beat rhythmically if we increase the number of its 
Na ions without increasing the number of its Caions. In 
one of the next papers it will be proved that the same result 
can be obtained more rapidly if we decrease the number of 
Ca ions in the muscle by precipitating them. 
3. The phenomena of muscular contractility and the phe- 
nomena of cell-division are considered by many authors as 
being of the same order. The rays of the astrosphere are 
said to be contractile fibrils which pull the chromosomes 
apart and accomplish the division of the mother-cell into 
two daughter-cells. I do not see how we can harmonize 
this hypothesis with the fact that enormous quantities of K 
ions in no way interfere with the process of karyokinesis, 
while even a much smaller amount of K ions annihilates 
muscular activity in a very short time. In the preceding 
paper I mentioned the fact that the ciliary motion of the 
blastulee of the sea-urchins continues in the presence of enor- 
mous quantities of K ions. The riddle of contractility is 
still unsolved. It yet remains to be proved that the ciliary 
motion and cell-division are due to contractile processes 
identical with those in the muscle. Our experiments on the 
effects of K ions should warn us against taking such an 
identity for granted. 
4. While a solution of NaCl with a small amount of K and 
Ca ions allows all the various vital processes to go on (except 
such special phenomena as the formation of the skeleton, 
with which we shall deal in the next paper), we find other 
combinations of ions which enhance some of the vital pro- 
cesses, while they prevent others. The most important com- 
bination in this direction is the mixture of $n KCl witha 
small amount of '?n CaCl,. In such a solution the first 
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