Figs. 19 and 20, plotted from the data of two of the experiments, show the relative heights of the threshold before and after an injection of adrenin. The close correspondence of the two readings of the threshold, one from the nerve supplying the muscle, the other from the muscle directly, served to show that there was no fault in the electrodes. The continuous line in the Figures represents the threshold (in units) of the muscle, the broken line that of the nerve-muscle. The threshold of the nerve-muscle is magnified 100 times in Fig. 19 and 10 times in Fig. 20. In Fig. 19 (at 2 and 4) the threshold was taken after an intravenous injection of 0.1 and 0.2 cubic centimeter of adrenin respectively. These examples show that adrenin does not affect the threshold of the normal non-fatigued muscle when tested either on the muscle directly or on the nerve-muscle. In Fig. 19 (at 3) the observation taken after two hours of rest illustrates the constancy of the threshold under these circumstances. In Fig. 19 the normal threshold was increased by fatigue (at 5)--the muscle had been pulling 120 times a minute for one hour on a spring having an initial tension of 120 grams--from 30.0 to 51.6 units, an increase of 72 per cent; and in the nerve-muscle from 0.62 to 0.89 units, an increase of 46 per cent. The threshold (at 6) was taken _five minutes_ after injecting 0.1 cubic centimeter of adrenin (1:100,000). The threshold of the muscle was lowered from 51.6 to 38.0 units, a recovery of 62 per cent; that of the nerve-muscle from 0.89 to 0.79 units, a recovery of 37 per cent. After another injection of 0.5 cubic centimeter of adrenin the thresholds (at 7) were taken; that of the nerve-muscle dropped to normal--0.59 units--a recovery of 100 per cent, and that of the muscle remained unaltered--26 per cent above its normal threshold. [Illustration: Figure 19.--A record plotted from the data of one experiment. The time intervals in hours and minutes are represented on the abscissa; the values of the threshold in β units are represented on the ordinate. The continuous line is the record of the muscle, the broken line that of the nerve-muscle. The nerve-muscle record is magnified 100 times; that of the muscle is normal. (1) Normal threshold stimulus. (2) Threshold five minutes after an intravenous injection of 0.1 cubic centimeter of adrenin (1:100,000) without previous fatigue. (3) Threshold after a rest of two hours. (4) Threshold five minutes after an injection of 0.2 cubic centimeter of adrenin (1:100,000) without previous fatigue. (5) Threshold after one hour’s fatigue. The muscle contracted 120 times per minute against a spring having an initial tension of 120 grams. (6) Threshold five minutes after an injection (0.1 cubic centimeter) of adrenin (1:100,000). (7) Threshold five minutes after another injection of adrenin (0.5 cubic centimeter of a 1:100,000 solution).]