124 



Blood Flow and Secretion 



Fig. 7.1. The effect of diminished blood supply on submaxillary secretion 

 evoked by chorda stimulation at maximal rate. 



Two different experiments are shown, the first three sections of the tracing being from one cat, 

 and the two last sections from another. Records of blood flow (lowermost) and secretion (above) 

 using ordinate recorders. Time marks: minutes. C marks the point where chorda stimulation 

 starts to continue for the rest of the period shown in each section. 



First section: Between the two marks of the signal the peripheral stump of the right vagus was 

 stimulated. 



Second section: The carotid artery was clamped. 



Third section: Sympathetic stimulated. 



In the second experiment the chorda was stimulated for the whole period shown. The first 

 signal marks the injection of 0-2 I.U. of pitressin, and the second 03 I.U. given close arterially 

 via the lingual artery (Emmelin, 19556). 



results as evidence for the existence of inhibitory secretory fibres 

 in the sympathetic. That this is not so, but that the decreased 

 secretion is secondary to the reduced supply of blood, is indicated 

 by the fact, shown in the figure, that various other procedures 

 which diminish the flow of blood through the gland have a similar 

 effect on the rate of secretion. It might be suggested that the re- 

 stricted flow in these instances favours the accumulation of acetyl- 

 choline to a concentration, sufficient to exert an inhibitory effect 

 on the gland cells (Graham and Stavraky, 1953) but it seems more 

 reasonable to assume for instance lack of water for secretion or of 

 oxygen as the decisive factor. The ''inhibitory" action of sym- 

 pathetic stimulation on the secretion is particularly easily obtained 

 when the gland is secreting at a maximal rate. 



In this connection an observation made by Denton (1957) is of 

 particular interest. When a sheep supplied with a permanent paro- 

 tid fistula was taken out of its cage and gently secured upon its 

 side on the laboratory table the secretion from the parotid gland 



