EXTERNAL INFLUENCES AS CAUSES OF VARIATION 277 



carbonate "one observes as a rule, after a longer or shorter period 

 of rest, that the immersed muscle begins to beat rhythmically'' 



On this point Loeb remarks that sometimes only a mere 

 tremor is noticeable, at others violent contractions ; that some- 

 times only individual fibers are active, at others the whole muscle 

 is involved; and that "at low temperatures these phenomena 

 may continue for days." 1 



These facts, together with Ringer's and Howell's statements 

 that calcium and potassium salts exert a direct action upon the 

 heart, led Loeb to extend the Biedermann investigations. He 

 subjected the gastrocnemius muscle of a frog (unweighted) to a 

 series of solutions of chemically pure materials in twice-distilled 

 water. 2 



These experiments not only confirmed Biedermann's findings 

 that the salts of sodium were able to excite rhythmic muscular 

 contraction but they also added lithium, caesium, and rubidium 

 to the list of bases, and the salts of bromin, iodin, and iron to 

 those of carbon, chlorin, and phosphorus. These movements 

 are periodic and continue into the second day, even at room 

 temperatures. 



Loeb determined that if a muscle be immersed in a 0.7 per cent 

 solution of sodium chlorid, contractions will begin in from sixty 

 to ninety minutes, but that " if a trace of alkali is added, con- 

 tractions begin much sooner." This acceleration he attributes 

 to the hydroxyl (OH) in the alkali added. Not only that, but r^ 

 ascribes the effect to the H involved in the hydroxyl, because 

 the same action follows the addition even of inorganic acids, as 

 HNO 3 , "if the same number of hydrogen ions are contained 

 in the unit volume"; 3 but Loeb hastens to assure us that 

 neither the hydrogen ions nor the hydroxyl ions " belong to 

 those which are capable of liberating rhythmic contractions." 

 They only accelerate the action of those which of themselves 

 possess this power. 



The action of sodium and other chemicals in exciting contrac- 

 tion is, in the opinion of Loeb, to be ascribed to their entering 



1 Loeb, Studies in General Physiology, Part II, p. 518. 

 ^ Ibid. pp. 519-538. 

 3 Ibid. p. 527. 



