To increase general arterial pressure two methods were used: the spinal cord was stimulated in the cervical region through platinum electrodes, or the left splanchnic nerves were stimulated after the left adrenal gland had been excluded from the circulation. This was done in order to avoid any influence which adrenal secretion might exert. It is assumed in these experiments that vessels supplying active muscles would be actively dilated, as Kaufmann[81] has shown, and would, therefore, in case of a general increase of blood pressure, deliver a larger volume of blood to the area they supply. The effects of increased arterial pressure are illustrated in Figs. 13, 14 and 15. In the experiment represented in Fig. 13, the rise of blood pressure was produced by stimulation of the cervical cord, and in Figs. 14 and 15 by stimulation of the left splanchnic nerves after the left adrenal gland had been tied off. The original blood pressure in Fig. 13 was 120 millimeters of mercury. This was increased by 62 millimeters, with a rise of only 8.4 per cent in the height of contraction of the fatigued muscle. [Illustration: Figure 13.--In this and the following records, the upper curve indicates the blood pressure, the middle line muscular contraction, and the lower line the time in 30 seconds (also zero blood pressure.) Between the arrows the exposed cervical spinal cord was stimulated.] In Fig. 14 the original blood pressure was 100 millimeters of mercury. By increasing this pressure 32 millimeters there resulted simultaneous betterment of 9.8 per cent in the height of muscular contraction. In Fig. 14 B the arterial pressure was raised 26 millimeters and the height of contraction increased correspondingly 7 per cent. In Fig. 14 C no appreciable betterment can be seen although the blood pressure rose 18 millimeters. [Illustration: Figure 14.--Stimulation of the left splanchnic nerves (left adrenal gland tied off) during the periods indicated by the arrows.] In Fig. 15 the original blood pressure was low--68 millimeters of mercury. This was increased in Fig. 15 A by 18 millimeters (the same as in Fig. 14 C without effect), and there resulted an increase of 20 per cent in the height of contraction. In Fig. 15 B the pressure was raised 24 millimeters with a corresponding increase of 90 per cent in the muscular contraction; and in Fig. 15 C 30 millimeters with a betterment of 125 per cent. [Illustration: Figure 15.--During the periods indicated in the time line the left splanchnic nerves were stimulated. The vessels of the left adrenal gland were tied off.]