SPECIFIC EXCITABILITY OF NERVE ENDINGS. Gii 



conditions of the centripetal neives belonging to the glands which we 

 had under consideration in our last lecture, or, more correctly, to find 

 out the conditions which excite the centres, as well ae the peripheral 

 endings of the different nerves, which form parts of the nervous appara- 

 tus of these glands. We have, therefoi e, for each phase of the work 

 of secretion, to find out that portion of the nervous mechanism which 

 is for the time being under excitation, and to discover the primary 

 agency by which this condition is elicited. This would include an 

 exact analysis of the stimulating influence which mastication and food 

 exert upon the nervous mechanism of these glands. We shall also be 

 able more fully to comprehend the inner mechanism underlying the 

 facts which formed the subject of the second lectui-e. This, of course, 

 is an ideal programme which we can only follow out as far as the present 

 state of physiology permits. It may now be instructive, and, for our 

 further conclusions, advantageous, to glance shoitly at the nervous 

 control of the salivary glands. 



The salivary glands, whose in nervation has long ago been investi- 

 gated, have generally been accepted as types of the deeper-lying 

 digestive glands, and when it became necessary to form a conception of 

 the mode of activity of the latter, medical science resorted to a bold 

 analogy and thought of the nervous apparatus of the salivary glands. 

 But the attempts of investigators to apply rigidly to otheis the scheme 

 of innervation which holds good for the salivary glands, have done 

 considerable harm to the usefulness of the analogy and have pre- 

 vented our arriving at a correct idea of the plan of innervation of the 

 abdominal glands. We have already had an example of this nature 

 before us. In the salivary glands we have no clearly marked indica- 

 tions of nervous inhibition, and this circumstance has decidedly retarded 

 the due development of our knowledge of the nervous control of the 

 abdominal glands. Authors naturally expected to see a simple and 

 prompt stimulation-effect from the same conditions of experiment which 

 sufficed for the salivary glands, and the failure of this gave them, as 

 they thought, the right to deny the existence of any extrinsic nervous 

 influence upon the abdominal glands. The erior is now obvious ; the 

 abdominal glands behave in some ways different from the salivary 

 glands, and for their successful investigation, other conditions of experi- 

 ment are necessary than those which held good for the former. In the 

 working of the abdominal glands nervous inhibitory processes play a 

 large part, but they are almost wholly absent in the case of the salivary 

 glands. This is an additional warning that one must never push the 

 conclusions drawn from analogy too far, but must constantly bear in 

 mind that the life-functions of all organs are extremely complicated, 

 and that the work of even the most apparently similar organs should be 



