INFLUENCE OF NERVES ON PANCREATIC SECRETION. 549 
Becretion ia still fairly marked, a further stimulation will result in 
inhibition of the secretion, which inhibition ends with the stimulation 
provoking it. The spontaneous secretion that is sometimes observed 
before the experiment begins, is stopped by cutting both vagi, and is 
therefore due to impulses proceeding from the upper portion of the 
cervical spinal cord or the medulla oblongata. Pawlow also points out 
the importance of the circulation in general for the secretion. A brief 
stoppage of the blood stream caused a cessation of the flow, and an 
anaemic condition of the gland resulting from reflex nervous influence 
caused a similar cessation. The latent period relapsing before the 
secretion resulting from stimulation becomes obvious, is, according to 
Pawlow, two to three minutes, but later observers such as Mette 1 and 
Kudrewetzkv 2 regard it as somewhat longer, namelv, from four to six 
minutes. Mette in addition found that, though previous observers 
(Lewaschew, Heidenhain) had stated that the proteolytic ferment failed 
in the pancreatic juice of dogs which had fasted five or six days, yet it 
was continuously obtainable by stimulation of the vagus. Gottlieb 3 
confirms the old observation, that stimulation of the divided vagus at the 
central end causes inhibition of the secretion, and he refers this result to 
general spasm of the abdominal blood vessels. Another contribution to 
the study of the inhibitory influences on the pancreatic secretion has 
recently been made by Popielski. 4 It had been previously noticed by 
Mette and Kudrewetzky that the secretion caused by stimulating one 
vagus could frequently be stopped by stimulating the other vagus. 
Hence it was inferred that antagonistic fibres passed in these nerves. 
Stimulation of such fibres may bring about sometimes a lengthened 
latent period, sometimes total inhibition of the flow. Mette regarded 
this as due to the existence of vaso-constrictor fibres, Kudrewetzky 
to the presence of specific fibres inhibiting the secretion. Popielski 
endeavoured to elucidate this point. He found that a secretion evoked 
by peripheral stimulation of the vagus could later, by a repetition of 
the stimulation of the same nerve, be interrupted. The interruption 
started some seven seconds after the stimulation commenced, and 
lasted about the same interval beyond the cessation of stimulation. 
This inhibition also follows from stimulation of the other vagus, as 
previously observed, and is best shown when the exciting current 
is not too strong. The branch of the vagus which lies behind the 
oesophagus in the thoracic cavity is that concerned with changes in 
the secretory activity of the pancreas. Dolinski 5 had previously 
observed that the introduction of acids into the duodenum produces 
a flow of pancreatic juice (see next section). Popielski made use of 
this fact to see how far the secretion thus excited could be inhibited 
by nerve stimulation. He found that a secretion so produced 
was inhibited with perfect regularity by stimulation of the vagus. 
Stimulation of the vagus, after secretion evoked by pilocarpine, pro- 
duced the same result. Popielski points out that there are three 
ways in which inhibition of the flow of pancreatic juice can be brought 
about — 
1. By stimulation of vaso-constrictor fibres. 
1 Arch. f. Physio/., Leipzig, 1894, Supp. Bd. - Ibid., 1894. 
3 Arch. f. exper. Path. it. Pharmakol., Leipzig, 1895, Bd. xxxiii. 
1 Centralbl.f. Physiol., Leipzig u. Wi/en, 1896, Bd. x. 
5 Arch, de sc. biol., St. Petersbourg, 1895, vol. iii. 
