822 CONTRACTION- WAVE IN MUSCLE 



described above was used. In both sets of observations the initial 

 speed is practically the same at about 20°C.; viz. about 7 cm. per 

 second. Both the old and the newer readings agree also in respect 

 to the rate and character of the changes undergone by the tissue 

 under the experimental conditions. After a period of 6 hours in 

 Ringer's solution the , transmission- velocity begins to be irregular 

 and the minimal stimulus in Ringer may fail to produce contraction. 

 Upon changing the tissue end for end, or cutting off a little of the 

 tissue on both ends, the regularity of response to the original minimal 

 stimulus is restored and the transmission-velocity recovers. The 

 strips of tissue selected for use have been from 3 to 5 mm. wide and 

 from 3.5 to 4.5 cm. long. The observation points were between 

 0.6 and 3 cm. apart. 



In 0.3 Ringer's solution strips of ventricle lose their irritability 

 in the course of about 2 hours, and in pure isotonic sugar solution 

 in about 50 minutes. Recovery of irritability upon replacement 

 in normal Ringer's solution occurs in about 2 minutes. Little differ- 

 ence has been observed between the propagation-velocities in freshly 

 prepared Ringer's solution and in older solutions through which 

 air was bubbled. 



The velocity of the contraction-wave is reduced in mixtures of 

 Ringer with sugar solution; but in solutions of less than 0.6 Ringer 

 the reduction of transmission-velocity is not proportional to the re- 

 duction in conductivity. Five experiments of the last series are 

 recorded in Table VII. 



DISCUSSION. 



The data presented in this paper lend further support to the thesis 

 that the electrical conductivity of the medium surrounding an ac- 

 tivated protoplasmic system is in direct correlation with the rate 

 of spread of the state of activation over the system. In skeletal 

 muscle, the contraction-wave travels along the fibers at a velocity 

 which is closely proportional to the electrical conductivity of the 

 fluid in contact with it. A reduction, by means of dilution with an 

 indifferent non-electrolyte solution, in the electrical conductivity of 

 the normal balanced medium is followed by a corresponding reduction 

 in the propagation-velocity of the contraction-wave. This parallelism 



