INHIBITORY NERVES TO THE VASCULAR SYSTEM 87 



Ludwig and his pupil Sadler were investigating the flow of 

 blood through muscles in a condition of rest and activity. These 

 investigations were continued by him with my assistance in 1874- 

 75, and showed most clearly how great was the increase of flow 

 through the muscle in consequence of the stimulation of its nerve. 

 About the same time Goltz had noticed that, whereas stimu- 

 lation of the sciatic nerve when fresh cut caused a diminution 

 of redness in the skin of the toes and a lowering of tempera- 

 ture as measured by a thermometer placed between the toes, the 

 same stimulation of the nerve, if cut two days before, gave a redden- 

 ing and an increase of temperature of the toes. He concluded 

 that vaso-dilator as well as vaso-constrictor nerves existed in the 

 sciatic and that they resisted degeneration for a longer time than 

 the vaso-constrictors. These observations of Goltz gave rise to a 

 number of other investigations made for the purpose of showing 

 the existence of these vaso-dilator nerves in the fresh-cut sciatic. 

 It was found by the method of rhythmical stimulation that the 

 dilator nerves could be excited with stimuli which failed to excite 

 the vaso-constrictors ; and further that reddening and rise of tem- 

 perature in the foot could occur to a well-marked degree, if only 

 the foot was cooled down sufficiently before the sciatic was 

 stimulated (Bernstein). 



Such were the main facts on which the existence of special 

 vaso-dilator nerves was based. 



The blood vessels alleged to be supplied by these vaso-dilator 

 nerves are divisible into three groups: (i) a group in which the 

 vascular dilatation is clearly coincident with the activity of the 

 organ ; this group includes all muscular and glandular organs ; 

 (2) the blood vessels of the skin, especially investigated in the 

 extremities, and (3) the blood vessels concerned with the pro- 

 duction of erection of the penis. 



I will consider first the increase in the flow of blood when 

 a muscle contracts. My experiments in Ludwig's laboratory 

 showed that the contraction of the muscle caused by direct com- 

 pression an outspurt of blood at the commencement of the con- 

 traction ; this was followed by a diminished outflow during the 

 muscular contraction and an enormous increase in the rate of 

 flow immediately after the contraction. If the contraction lasted 

 some time, the increase of flow might commence while the muscle 



