534 STUDIES IN GENERAL PHYSIOLOGY 



in this not allow the statements of the botanists to lead ns 

 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. 1 

 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. In a 

 Na 2 SO 4 solution the contractions cease in less than two 

 hours. The aiiions of the given salts diminish very markedly 

 the irritability. In Na 3 PO 4 no contractions whatsoever 

 occur, and here the irritability is reduced very rapidly. 

 The same holds also for Na 2 CO 3 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 4 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 



i R. H. TRUE, Botanical Gazette, Vol. XXVI (1898). 



