CIRCULATION IN SKELETAL MUSCLE 1 36 1 



fig. 8. Typical tracing obtained by Mellander using the preparation shown in fig. 7. For further 

 explanation see text. [After Mellander (149).] 



was a measure of the decrease in the volume of blood 

 in the hind limbs, mainly due to contraction of the 

 venules. The subsequent slower shrinkage, indicated 

 by the dotted sloping lines, was a measure of the 

 rate of loss of tissue fluid. Below the record of the 

 volume changes are shown the corresponding changes 

 in capillary pressure; these were calculated after the 

 experiment and will be referred to later. Below this 

 again we see the changes in the venous outflow from 

 the hind parts, the rate of flow is proportional to the 

 height of the record. At the beginning of the experi- 

 ment the venous pressure was adjusted, by raising 

 or lowering the venous outflow cannula, so that the 

 volume of the hind parts remained constant. It 

 will only be necessary to consider the change in the 

 circulation produced by sympathetic nerve stimula- 

 tion at 2, 8, and 16 impulses per sec. Typical results 

 are shown in table i . The data obtained from the 

 tracing are shown by the figures in italic, namely 

 the arterial blood pressure (line i); the capacitance 

 changes (initial rapid shrinkage, line 8); the rate of 

 loss of tissue fluid (slow continuous shrinkage, line 

 12) and the rate of the venous outflow (line 2). 



It will be convenient to consider first the changes in 

 resistance due to the effect of the vasoconstrictors in 

 the precapillary and postcapillary vessels, that is 

 mainly on the arterioles, and to a smaller extent on 

 the venules. Maximal vasoconstriction was produced 

 by stimulation at frequencies of 16 per sec or more. 



The outflow decreased from 60 to 10 ml per min 

 (line 2), a reduction of 50 ml (line 3) which can be 

 regarded as 100 per cent maximal (line 4). This 

 corresponds to a 6-fold increase in resistance (line 5), 

 an increase of from 2 to 12 P.R. units (line 6). 



However the maximum possible physiological 

 impulse frequency, as we shall see, is probably not 

 more than 6 to 10 per sec. The changes recorded 

 using a frequency of 8 per sec are therefore of par- 

 ticular interest. The blood flow from the hind parts 

 was reduced from 60 to about 13 ml (line 2), a reduc- 

 tion of about 47 ml (line 3), a response corresponding 

 to g4 per cent of the maximal (line 4) and to a four- 

 and-a-half-fold increase in resistance (line 5). These 

 figures correspond to a reduction in the rate of flow 

 in the hind parts from 8.5 ml per 100 ml hind part 

 per min to 1.85 ml per 100 ml per min (hind-part 

 volume 700 ml). 



We must now refer to the effects of stimulating the 

 vasoconstrictor nerves upon the volume of blood 

 in the vessels of the hind parts. The maximal effect 

 was obtained at a frequency of 8 per sec. At this 

 frequency, 6.25 ml were expelled by venous contrac- 

 tion (table 1 : line 8). According to this the amount of 

 blood that could be expelled by venous contraction 

 from the whole of the skin and the entire skeletal 

 muscular system, tissues weighing half as much as 

 the whole body, would be only 4.5 per cent of the 

 animal's blood volume. But of course it must be 



