548 MECHANISM OF SECRETION OF PANCREATIC JUICE. 



centre for pancreatic secretion, as, after its separation from the cervical 

 spinal cord, the secretory process can continue, although with diminished 

 intensity. 



4. The nerves proceeding to the pancreas do not seem to have the 

 same direct influence upon the secretion that the nerves to the salivary 

 glands possess. 



5. Stimulation of the central end of the divided vagus, according to 

 Bernstein, 1 or of sensory nerves in general (e.g. cutaneous), according to 

 Afanassiew and Pawlow, 2 may inhibit the secretion, provided the pan- 

 creatic nerves are intact. This, Heidenhain regards as due to vascular 

 changes. 



Pawlow 3 found that the administration of atropine stopped the 

 secretion frequently, but not in all animals (e.g. in dogs but not in 

 rabbits), and Heidenhain observed that the administration of pilocarpine 

 caused a sluggish secretion of a concentrated juice. 



The later experiments of Pawlow and the St. Petersburg school have 

 greatly amplified our knowledge of the nervous influence. In Pawlow's 

 further researches he observed the effects of nerve stimulation upon dogs 

 prepared for experiment in two different ways. In the first case the 

 dog had a permanent pancreatic fistula prepared, one vagus in the neck 

 was also divided. The stimulation of the peripheral stump of the vagus 

 was performed some five days after the section, at a time when certain 

 fibres in the vagus had degenerated. In the second case the vagus was 

 cut through in the neck, and after three or four days the animal was 

 prepared for experiment by the performance of tracheotomy, section of 

 the spinal cord just below the medulla oblongata, and the preparation of 

 a fresh pancreatic fistula. In both these cases stimulation of the peri- 

 pheral end of the vagus causes secretion from the pancreas. Moreover, 

 stimulation of the intact vagus also produces this result, and even if 

 neither vagus is divided a more or less pronounced secretion ensues. 

 Certain differences are observable, however, between the general effects in 

 the two cases. In the first case more secretion was produced, this being 

 comparatively watery in character and greatest in amount at the 

 commencement of stimulation. These differences are probably accounted 

 for by the general low blood pressure in the second case. The pressure 

 of the secretion was found by Pawlow to be lower than the corresponding 

 blood pressure, and it was noted that vagus stimulation in one case still 

 caused a secretion, although the blood pressure was reduced by bleeding 

 practically to nil. Frequently the secretion would end with the lowering 

 of the blood pressure, but nevertheless the one experiment is sufficient 

 to establish the independence of the secretion of the blood pressure. 

 The action of atropine is to cause a marked influence on the effects 

 of nerve stimulation, though complete cessation of the secretion is not 

 produced. Reflex effects can be produced on the secretion, which do nob 

 correspond to the effects upon the blood vessels. Stimulation of the 

 central stump of the lingual or of the vagus nerve will produce such reflex 

 effects. If, at the commencement of the experiment, either 110 secretion 

 or a slight secretion occurs, with the first stimulation of sensory nerves 

 either a commencement or an increase of the secretion results. After 

 the stimulation ceases this lessens. If after the first stimulation the 



1 Ber. d. k. sacks. Gesellsch. d. JFissensch., Leipzig, 1869. 

 ' 2 ArcTi.f. d. yes. Physiol., Bonn, 1878, Bd. xvi. 

 z Arch.f. Physiol., Leipzig, 1893, Supp. Bd. 



