THE SYMPATHETIC SYSTEM 299 



is concerned, it is not necessary to invoke the direct action 

 of this system on cellular elements. 



We know that the true sympathetic acts upon the vaso- 

 motor system and also that it plays a part on the 

 production and liberation of hormones. Two different 

 hypotheses can, therefore, be brought forward as regards 

 the action of the true sympathetic on metabolism. It is 

 possible that circulatory changes occur within organs 

 which cause changes in the glandular functions of the 

 cells. This probably explains certain of the phenomena, 

 but not all. We must, therefore, in order to explain these 

 refer to the action of the hormones, by their direct and 

 indirect action on the glands of internal secretion. 



As regards the phenomenon of inhibition produced by 

 stimulation of sympathetic fibres, here again circulatory 

 changes play a part and we must not forget, that according 

 to the latest findings, the mechanism of inhibition does 

 not necessitate inhibitory fibres. These phenomena can 

 be entirely due to changes in the contact of the nerve and 

 the tissue and which may occur in any stimulating fibre, 

 providing the articular membrane of the neuron is in a 

 proper physicochemical condition. 



If we, therefore, look at the enervation of the true 

 sympathetic as a whole we see that it is primarily vascular 

 (smooth muscles of the blood vessels) and dermic (smooth 

 muscles of the skin glands). In a rather ingenious hypoth- 

 esis, which, however, must be studied and confirmed, 

 Gaskell considers the digestive sphincters as a supple- 

 mentary covering of the gastro intestinal tract, which has 

 nearly disappeared and which left only remains in the 

 shape of the sphincters. This tunic, according to Gaskell, 

 is also dermal in origin, 11 and this is why he calls the true 

 sympathetic the vaso-dermal system, believing, as does 



11 Certain recent embryological researches seem to confirm Gaskell's theory. 



