1 1 4 THE INVOL UNTAR Y NER VO US S YSTEM 



method, in as close connexion with the fibres of the vagus nerve 

 as are the cells of Remak's, Ludwig's and Bidder's ganglia in the 

 case of the frog's heart. Manifestly such cells are the motor cells 

 of the vagus system. In the case of this low form of fish, they 

 are the only manifest cells to be found. Recently Sakuseff has 

 investigated at Dogiel's suggestion the nature of Auerbach's 

 plexus in the Teleosteans, Chondropterygians and Cyclostomes, 

 by the methods of Golgi and Ehrlich, and has found in the two 

 former classes offish the two types of cells described by Dogiel, 

 but in the cyclostomes only one kind of nerve cell, which belong 

 to Dogiel's Type II. 



Further Dogiel has traced from the cerebro-spinal or vagus 

 nerves fibres which terminate by arborizations round nerve cells, 

 and he finds such fibres traverse many ganglia and give off 

 collaterals to their cells ; he does not state the type of cell around 

 which they arborize, because, as a rule, when the staining allows 

 cerebro-spinal nerve fibres to be traced a long way, the cells are 

 not stained, but, judging from the evidence of the cyclostomes, 

 they must be cells of Type II. Finally the body of the cell of 

 Type II is round, rather than angular, and its processes of clean 

 unbranched nerve fibres pass away from the ganglia along the 

 bundles of nerve fibres which form the plexus, to end, according 

 to Cajal, around the muscular or glandular cells. 



Fixing then our attention on Type II alone, we see that in 

 every respect the innervation of the gut is of the same character 

 as that of other organs innervated by the involuntary nervous 

 system ; the vagus fibres are connector fibres which, as in other 

 cases, connect with many cells by means of collaterals, and these 

 cells are the motor cells to that part of the gut musculature which 

 belongs to the vagus system. There is no question of the sym- 

 pathetic fibres connecting with such cells ; they pass through the 

 ganglia, as described by Cajal, and do not connect with any nerve 

 cells but go direct to muscles. 



In another respect these motor cells in the alimentary canal 

 resemble other motor cells of the involuntary system. The tone 

 of the muscle normally depends upon them. Cannon has 

 shown that in the stomach a tonically contracted band is seen 

 at the incisura'cardiaca during digestion, from which rhythmical 

 contractions start and travel along the antrum to the pyloric end. 

 These rhythmical contractions depend upon a certain condition 



