PAW LOW'S RESEARCHES. 493 



Pawlow has pointed out two methods by which these 

 aims may be accomplished. In the first method a per- 

 manent pancreatic fistula is established, and at the same 

 time one vagus is exposed in the neck, ligatured and divided. 

 The ligature is left hanging from the wound, so that at any 

 subsequent period the nerve may be drawn out and stimu- 

 lated without any discomfort to the animal. Three days 

 afterwards, without any preliminary anaesthesia, the cut 

 vagus is stimulated with any ordinary faradic current. The 

 invariable result of the stimulation is a secretion of pancreatic 

 juice which Mows from the fistula and can be collected in the 

 usual way. The latent period intervening between stimu- 

 lation and secretion varies between fifteen seconds to two 

 or three minutes. No effect is produced on the cardio- 

 vascular system, the inhibitory nerves having degenerated 

 in consequence of the section. Injection of atropin stops 

 secretion, and prevents the effect of stimulating the vagus. 



In the second method, the preliminary operation is dis- 

 pensed with. In this case it is of course necessary to prevent 

 the inhibitory impulses, which are started by the operative 

 stimulation of sensory nerves, from reaching the gland. 

 To this end, Pawlow, in the unanaesthetised animal, rapidly 

 performs tracheotomy and division of the spinal cord just 

 below the medulla, these two operations in his hands 

 not occupying more than half a minute. The impulses 

 which inhibit secretion seem to act reflexly through the 

 medulla, so that they are in this way cut off from the gland. 

 He then resects three or four ribs in order to expose the vagi 

 below the point where they give off their cardiac branches, 

 and finally makes a temporary pancreatic fistula. Stimula- 

 tion of the vagi below the heart now gives rise to a secre- 

 tion or increases the secretion already present. Using this 

 method it is better to stimulate the vagi mechanically by 

 means of Heidenhain's tetanomotor or to use single in- 

 duction shocks at intervals of one second, instead of the 

 faradic current. 



The reason for this superiority of single shocks over the 

 faradic current possibly lies in the fact that the vagus may 

 include vaso-constrictor fibres to the pancreas. Pawlow 



