8o . DYNAMICS OF LIVING MATTER 



this effect only through the diffusion of NaCl into the muscle. As 

 soon as the concentration of the NaCl or the Na-ions in the muscle 

 has reached a certain value, the muscle fiber will begin to contract. 



Normally the quotient —^ in the muscle is too small to permit such 



Cca 



contractions. The addition of a slight amount of NaHO accelerates 

 the process, possibly by accelerating the diffusion of the salt into the 

 muscle.* 



The fact that CaCl^ inhibits the rhythmical contractions which are 

 produced by the NaCl, suggested experiments on the effects of salts 

 which precipitate Ca or diminish the concentration of free Ca-ions 

 through the formation of salts with a low degree of dissociation. It 

 was found that such salts, e.g. sodium-oxalate, -fluoride, -citrate,' and 

 -tartrate, act much more powerfully than NaCl or sodium-acetate or 

 -succinate. If such salts be applied to the nerve they produce before 

 the twitchings begin a condition of increased irritabihty, comparable 

 to the catelectrotonic condition caused by the constant current at the 

 region of the cathode.f 



The addition of a slight amount of acid to a -^ NaCl solution shortens 



o 



the latent period for the beginning of the rhythmical contractions. 

 We shall see later on that the acid acts possibly hke the above-mentioned 

 salts; namely, by Hberating the calcium from certain organic combi- 

 nations in the muscle or nerve. Inasmuch as CO^ is produced in the 

 muscle itself, this relation is of importance. 



These facts suggested the idea that the process of contraction is 

 caused by an exchange of Na or K for Ca or Mg, or vice versa, in cer- 

 tain compounds in the muscle (or nerve). This change must be accom- 

 panied by a change in some physical property of the compound, e.g. 

 the surface tension, the state of aggregation, viscosity, absorbing power 

 for water, etc. The change in such a physical property may deter- 

 mine or facihtate the process of contraction. 



I applied the facts found in the muscle to the study of rhythmical 

 contractions in a more favorable object; namely, the swimming 

 bell of the Medusa. The jellyfish is comparable to a free-swimming 

 heart which beats rhythmically, with this difference, however, that the 

 jellyfish does not beat incessantly, like the heart, but intermittently, 

 with long pauses between series of contractions. It is known that the 

 central nervous system of the Hydromedusa is situated in a ring near 

 the edge of the Medusa. Romanes had already observed that if the 



* Loeb, Festschrift fiir Fick, Wiirzburg, 1899. 



t Loeb, Am. Jour. Physiology, Vol. 5, p. 362, 1901. PflUger's Archiv, Vol. 91, p. 248, 

 1902. 



