62 THE INVOLUNTARY NERVOUS SYSTEM 



system are found close against the muscles themselves, whether 

 they have travelled out from the bulbar or the sacral regions, 

 whether they are supplying with motor fibres the endodermal 

 muscles in the small or large intestines, in the bladder, in the 

 lungs or in the liver (Fig. 5). 



Just as the sympathetic vasodermal musculature has invaded 

 the endodermal musculature to form the sphincter of the gut, so> 

 also has the endodermal musculature invaded the vasodermal 

 musculature in the case of the heart, as described on p. 80. 



In the last chapter I pointed out that the sympathetic or 

 vasodermal musculature formed a natural group, because the motor 

 activities of those muscles were alone picked out by adrenalin. 

 Now Dale has found that a substance obtained from ergot, which 

 Ewins working with him has identified as acetyl-choline, when 

 injected intravenously in very minute doses, produces the same 

 effects as stimulation of the bulbo-sacral connector nerves ; 

 just as adrenalin injected intravenously in very minute doses 

 produces the same effects as stimulation of the thoracico-lumbar 

 connector nerves. Considering then at present only the motor 

 actions produced by acetyl-choline, we see that it picks out the 

 endodermal musculature just as adrenalin picks out the sym- 

 pathetic or vasodermal musculature. 



I conclude that, in considering the nature of the innervation 

 of involuntary muscle, it is wrong to look upon all unstriped 

 muscle as of the same kind ; the unstriped musculature must be 

 classified into groups, which differ from each other morphologic- 

 ally and also in all probability histologically ; thus, as already 

 mentioned, Kalischer looks on the vasodermal musculature as 

 different in structure to the endodermal musculature, judging 

 from the structure of the bladder. 



Before proceeding to discuss the evidence for a system of 

 inhibitory nerve cells and nerve fibres and glandular nerves, it 

 will be well to sum up the conclusions already arrived at with 

 respect to the purely motor part of the involuntary nervous 

 system. The}' may be stated broadly as follows : 



The motor cells of the involuntary muscles have left the 

 central nervous system to form the various peripheral cell groups, 

 while the motor cells of the voluntary system have remained in 

 the central nervous system ; the axons from these latter form the 

 ordinary motor nerves of striated muscles, the axons from the 



