MOTOR FUNCTIONS OF THORACICO-LUMBAR OUTFLOW 47 



We may then sum up the results of this chapter as follows : 

 The motor cells of the so-called sympathetic system, which are 

 connected with the central nervous system by the thoracico- 

 lumbar outflow of connector nerves, form that part of the in- 

 voluntary system which supply <4notor nerves to all the muscles 

 of the vascular system and to a ' dermal ' system of muscles 

 originally lying under the skin. This dermal system is divisible 

 into three groups : 



1. The dermal or ectodemnal system proper, the motor cells of 

 which are in all cases situated in the lateral sympathetic ganglia, 

 and send motor fibres to all the involuntary muscles in the body, 

 which are still lying just under the skin. 



2. The uro-genito-dermal system, the motor cells of which are 

 in all cases situated in or near the muscles themselves and send 

 motor fibres to all the involuntary muscles which originally sur- 

 rounded the Wolffian and Miillerian tubes. 



3. The alimentary canal system, the motor cells of which are 

 in all cases situated in the mesenteric ganglia, and send motor 

 fibres to sympathetic muscles which have helped to form the new 

 gut, and still exist as sphincters in that gut. 



There is thus, it seems to me, evidence of a marked unity in 

 the sympathetic nervous system, which separates it from the other 

 members of the involuntary system, and such unity is further 

 shown by the extraordinary action of adrenalin. Oliver and 

 Schafer discovered that an extract of the supra-renal glands in- 

 jected into the circulation caused a rise of blood pressure due 

 to the contraction of the muscles of the blood vessels, and that the 

 substance which caused this effect was contained in the medul- 

 lary and not in the cortical portion of the gland. The substance 

 in question was subsequently isolated by Takamine and has re- 

 ceived the name of adrenalin, adrenine, or epinephrin. Its con- 

 stitution is now known. 



Since this discovery a large amount of work has been done 

 on this subject especially by Lewandowsky, Langley, Elliott, 

 Biedl, and others, which has firmly established the following 

 conclusion. Adrenalin acts only on those tissues which are in- 

 nervated by the sympathetic nervous system, and its action is al- 

 ways the same as that of the sympathetic nerves supplying the 

 tissue. If their stimulation causes contraction then adrenalin 

 causes contraction, if it produces inhibition, so does adrenalin. 



