The respiratory rate of the nerve cord of Cambarus clarkii

The rate of production of CO₂ of the nerve cord of Cambarus was determined by means of the colorimetric method previously described. 2 The nerve cord was removed entirely freed from other tissue. Stimulation due to cutting was only momentary. It could be shown, by leaving the cord attached at the anterior end, that irritability was retained by the posterior dissected portion of the cord for more than 45 minutes. Since it is possible to complete a respiration experiment in 20 minutes, the tissue must have been irritable throughout each experiment.

The procedure consisted first in determining the rate of CO₂ output for the resting cord. The effect of activity on the respiratory rate was found by suspending the tissue in the indicator tube on platinum electrodes which were passed through a paraffined stopper, and then stimulating the cord with induction shocks while the reading was being made. The current used for this purpose was not sufficient of itself to cause any change in the tint of the indicator, no matter how long continued. A third reading was now made with the tissue at rest. The relative rates of respiration in the three cases were determined by calculating the second and third readings as per cents. of the first. Averages of ten experiments made on the nerve cords of as many different animals yielded the following result: Resting IOO per cent., stimulated 89 per cent., resting 86 per cent. Electrical stimulation, therefore, not only did not increase the rate of CO₂ production of the nerve cord of Cambarus, but failed to interrupt the normal fall in rate. The question may thus rightly be raised whether functional activity of the cells of the central nervous system of the cryfish is accompanied by increased metabolic activity.