1 82 BIOLOGICAL LECTURES. 



the cell goes to pieces, nor the secretion by budding, nor the 

 explosion of the cell by turgor. Indeed, the secretory nerves, 

 like the epicycle, are hypothetical existences devised to explain 

 certain facts. What are those facts } If we can explain them 

 without assuming the existence of such nerves, the hypothesis 

 loses its value. 



The most important fact is the action of atropine. If atro- 

 pine be injected into a dog, vaso-dilation will still ensue on 

 stimulation of the chorda tympani nerve, but no secretion from 

 the submaxillary. This shows, says Heidenhain, that vaso- 

 dilation by itself is not able to cause secretion. This inference 

 is, as will be seen, entirely unwarranted, since it is quite possi- 

 ble, and is, I believe, undoubtedly true that vaso-dilation always 

 causes secretion in the normal gland, but not in that poisoned 

 by atropine. Atropine might have acted on the capillary 

 walls, preventing the exudation of lymph. That it does so act 

 there can be hardly a doubt. It might act on the gland cells, 

 preventing them in some way from secreting in spite of vaso- 

 dilation. Why was the latter, the natural explanation, not 

 adopted .'' Because it was assumed that there was but one 

 mechanism of secretion. There is but one mechanism of 

 secretion, says Heidenhain. The sympathetic, hence, causes 

 secretion in the same manner as the chorda. But the sympa- 

 thetic is not paralyzed by atropine ; therefore, as the sympa- 

 thetic innervates the gland cells, these have not been paralyzed. 

 But if the gland cells have not been paralyzed, and the dilator 

 function of the chorda is unaffected, and atropine does not act 

 on the nerve fiber, then the drug must paralyze the nerve ends 

 of the hypothetical secretory nerve endings. The final false 

 inference from three erroneous, or unproven, assumptions ! 

 This one example will suffice to show the character of the evi- 

 dence of the existence of separate secretory nerves. Outside 

 of the salivary glands of mammals there is no evidence worthy 

 of the name of the existence of such nerves. It is only in 

 those glands in which the muscle and gland cells are most 

 closely intermingled, and relationships the most obscure, that 

 such evidence can be found. It is to the writer almost incred- 

 ible that so far-reaching and fundamental an hypothesis should 



