THE PHYSIOLOGY OF SECRETION. 181 



sense originally used by Ludwig the nerves ought not properly 

 to have been called secretory nerves ; they correspond exactly 

 to Heidenhain's " trophic" nerves. If we mean, when we 

 speak of secretory nerves, secretory nerves in Ludwig's sense, 

 as is, I believe, generally meant, then all talk of secretory 

 nerves affecting a special secretory power of the cell is wrong. 

 They had no direct influence whatever on any hypothetical 

 secretory power of the cell. Heidenhain, who put the Ludwig 

 theory on its present pedestal, adopted a new sort of nerves. 

 Those which acted on the cells, rendering their contents solu- 

 ble and thus affecting osmosis, he called " trophic " nerves ; he 

 postulated an entirely new sort of fiber which did act on the 

 secretory power of the cell. These were the secretory fibers. 

 They had no influence at all on the chemical processes of the 

 cell, but only affected the resistance to filtration of the inner 

 end of the cell. If we use the term " secretory " nerve in 

 Heidenhain's sense, we can speak of their affecting the secre- 

 tory power of the cell. Some physiologists use the term in 

 one sense, some in another. This last theory of Heidenhain's 

 is one of the most extraordinary, to designate it by no harsher 

 term, of all physiological theories. It necessitates the conclu- 

 sion that each single cell of the submaxillary gland, for exam- 

 ple, has acting on it at least four different nerve fibers, i.e., 

 the trophic of the sympathetic, the trophic of the chorda tym- 

 pani, the secretory of the sympathetic, and the secretory of the 

 chorda tympani. With such consequences the Heidenhain 

 theory is undoubtedly false. But are we in any better position 

 if we follow Ludwig ? Suppose we relinquish the trophic 

 fibers and adopt the customary fashion of speaking glibly of 

 secretory fibers. How do these nerves act ? Do they act, as 

 Ludwig thought, by producing chemical changes in the cell, in 

 which case they do not directly affect any secretory function 

 of the cell, or do they act in the Heidenhain sense on the inner 

 border of the cell? It is all very well to speak of secretion, 

 secretory activity, secretory nerves. In science definite mean- 

 ings must be assigned the terms used. Just which of the 

 secretory mechanisms are to be governed by such nerves ? 

 Certainly not the secretion of milk, in which the whole end of 



