584 STUDIES IN GENERAL PHYSIOLOGY 
in this not allow the statements of the botanists to lead us 
astray. We have in the contractile and rhythmically acting 
animal tissues much more sensitive living reagents than the 
botanist has in most plants. True has also recently found 
that NaCl is not an indifferent substance. He attributes, 
however, a purely osmotic effect to the pure sugar solutions.’ 
This is, however, incorrect for animal tissues at least. 
12. Naturally ions which decrease the irritability must 
always counteract the effects of an ion capable of calling 
forth contractions when both are present in the solution. 
That can be best understood when a large number of Na 
salts are prepared which are equimolecular with a 0.7 per 
cent. NaCl solution. In nearly all of these solutions 
rhythmical contractions occur at first. It is dependent 
only upon the anion how long these contractions continue. 
While the contractions in a NaCl or NaBr solution may 
last from twenty-four to forty-eight hours, they cease in an 
isotonic solution of sodium acetate, butyrate, oxalate, tar- 
trate, or citrate in one-half to one and a half hours. Ina 
Na,SO, solution the contractions cease in less than two 
hours. The anions of the given salts diminish very markedly 
the irritability. In Na,PO, no contractions whatsoever 
occur, and here the irritability is reduced very rapidly. 
The same holds also for Na,CO, equimolecular with a 0.7 
per cent. NaCl solution. Hydrogen and hydroxyl ions also 
decrease the irritability, even in very dilute solutions. The 
same is true of NH, ions. 
13. I believe that these and similar facts will help us to 
understand the phenomena of contraction, and possibly also 
the phenomena of irritability in general. I will only show 
in this paper that the conclusions which we have drawn hold 
also for heart muscle. Aubert has found that the ventricle 
will beat in a physiological NaCl solution, but that it is not 
1R. H. True, Botanical Gazette, Vol. XXVI (1898). 
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