80 THE WORK OF THE DIGESTIVE GLANDS. 



the secretion is completely arrested. If, instead of the electric current, 

 mechanical stimulation (for example, a series of taps with Heidenhain's 

 tetanometer) be employed, a different result is to be observed : a little 

 time after the beginning of the excitation a tolerably strong secretion 

 sets in. The same may be obtained by means of electrical stimulation, 

 not, however, with a fresh nerve, but with one which has been divided 

 three or four days before, and which, in consequence, is partially dege- 

 nerated. The meaning of these events is easy to understand when 

 one calls to mind a few facts from the physiology of the vascular nerves. 



We know that vaso-constrictor nerves are much less sensitive to 

 mechanical stimuli than many others, and lose their irritability much 

 earlier after division. We may, therefore, correctly assume (1) that 

 both vaso-constrictor as well as secretory fibres for the pancreatic gland 

 run in the sympathetic nerve ; (2) that in ordinary electric excitation 

 the vaso-constrictor effects completely mask the secretory ; and (3) that 

 only under special conditions which eliminate the activity of the vaso- 

 constrictor nerves (e.g., mechanical excitation, or the application of the 

 electric current to a previously divided nerve) can the secretory fibres 

 manifest their effects. 



In the case of the sympathetic nerve we are now able to recognise 

 clearly the mutual relationship which exists between the vaso- 

 motor and secretory fibres of the pancreas. Our opinion regarding 

 the effect of the vagus upon the glands has suffered, however, 

 no alteration as a result of the employment of the special modes of 

 stimulation mentioned above. Its inhibitory effect upon the secretion 

 remains to the full. This gives us good reason for believing that the 

 influence of the vagus in question, does not depend upon a contraction of 

 the vessels. The question with which we are dealing has recently made 

 an important advance, thanks to the work of Dr. Popielski. He has, in 

 the first instance, worked out a plan of experiment in which the inhibi- 

 tory effect of the vagus upon the pancreas is shown in a constant 

 and striking manner. During the acute experiment already described 

 a solution of hydrochloric acid is poured into the duodenum. By this 

 means a long- continued and vigorous secretion of pancreatic juice is 

 called forth. If the vagus nerve be now strongly stimulated, a slow- 

 ing often to complete standstill of the secretion is obtained every 

 time without exception. Excitation of the sympathetic, on the other 

 hand, only slows the secretion, and this after the lapse of some time. 

 A compression of the aorta arrests the secretion only after two to three 

 minutes. To this it must be added that, according to the last experi- 

 ments of Francois Frank, the vagus nerve dilates rather than constricts 

 the vessels of the pancreas. The possibility of simultaneous action on 

 the part of the motor nerves to the excretory ducts was excluded by 



