810 CONTRACTION-WAVE IN MUSCLE 



Method. 



The velocity of the contraction-wave in muscle, i.e., of the trans- 

 mission of the excitation state, is measured by recording the time of 

 the bulging of a strip of tissue at two or more points along its length 

 as it undergoes contraction. In the present investigation the local 

 bulging is made to operate (by a simple lever system) minute mirrors, 

 which bring to focus upon a moving photographic film mirror-images 

 of an illuminated slit. The muscle is either stimulated at one end 

 by a minimal "break" induction-shock, or (as in the Limulus heart) 

 it is rhythmically beating and the contraction-wave moving along 

 the tissue operates the mirrors as it passes certain points. Each organ 

 or strip of muscle while fixed in place for experimentation is arranged 

 so that without otherwise changing the conditions it may be exposed 

 to a succession of solutions of graded electrical conductivity; e.g., 

 mixtures of sea water or Ringer's solution with isotonic sugar solu- 

 tion in varying proportions (1:9, 2:8, 3:7, etc). An electrically ac- 

 tuated tuning-fork of suitable frequency, with an attached mirror, 

 is so arranged that a time curve is recorded upon the moving film 

 above the muscle record. The solutions used with turtle and frog 

 tissues have been corrected to, or kept at, constant temperature, 

 about 20°C., and the hydrogen ion concentration of the solutions 

 has been adjusted before experimentation to that of the Ringer's 

 solution employed in the same series; i.e., about pH = 6.8. Measure- 

 ments of the hydrogen ion concentrations have been made by the 

 colorimetric method of Clark and Lubs with standardized buffer 

 solutions." The electrical conductivity of the solutions in all the 

 work has been measured at 25°C. by the method of Kohlrausch, 

 determinations being made immediately before and after taking the 

 muscle record. 



The apparatus which has been used in this study for recording the 

 passage of the contraction-wave is specially constructed so as to allow 

 the external medium to be changed at will without otherwise dis- 

 turbing the tissue. It is described in detail by the author elsewhere. 

 The supporting part of the apparatus coming into direct contact 

 with the frog and turtle tissues is entirely composed of vulcanized 



" Clark, W. M., The determination of hydrogen ions, Baltimore, 1920, 38ff. 



