SECRETION PHYSIOLOGY. 295 



Heidenhain, R. Ueber secretorische und trophische Drilsennerven, Pfliiger'' s 

 Archv. f. d. gesam. Physiologie. Bd. XVII, 1878, pp. 60 and following : ''The 

 cell is normally under high endosmotic pressure. On nerve stimulation a 

 molecular rearrangement takes place at the lumen end of the cell, so that the re- 

 sistance to filtration is diminished and water flows out. This flow may be hastened 

 by contractions of the protoplasm, as Kiihne observed in the rabbit's pancreas under 

 the microscope. The tension of the water within the cell being thus diminished, 

 water begins to flow out of the lymph and capillaries into the cell. At the end of 

 stimulation molecules are rearranged, the loss of water by the cell ceases, and se- 

 cretion stops." *' The attractive pull on the water comes from the protoplasm of 

 the outer zone." 



Before proceeding with the discussion of the evidence upon 

 which this theory rests, it will make the matter clearer to recall 

 the conception of secretion which the Ludwig-Heidenhain 

 theory supplanted. For some of the facts brought forward by 

 these authors are of value, not as direct evidence of the exist- 

 ence of secretory nerves, but because they disprove an alterna- 

 tive earlier conception. The prevalent conception of secretion, 

 before Ludwig's time, was that liquid driven by intra-capil- 

 lary pressure filtered out through the gland/^ The chorda 

 tympani was the principal secretory nerve then known, and it 

 was believed to cause secretion by greatly increasing intra-ca- 

 pillary pressure by contraction of the veins or arterioles. The 

 discovery of the vaso-dilator function of this nerve shortly 

 thereafter by Claude Bernard re-emphasized the possibility of 

 a high intra-capillary pressure being an essential cause of secre- 

 tion. It is not surprising that many physiologists of that day 

 believed that this striking correspondence between vaso-dilation 

 and secretion could not be accidental, and it was natural for 

 them to refer the secretory power of the nerve to its action on 

 the blood vessels. 



The first blows against the theory that the vascular system 

 stood necessarily in a causal relation to secretion were dealt by 

 Ludwig and his pupils. They discovered that stimulation of the 

 upper end of the cut cervical sympathetic nerve caused a secretion 

 from the submaxillary gland of the dog,^^ but this secretion, un- 

 like that due to the chorda, was afterwards found to be accom- 

 panied by a pronounced vaso-constriction instead of dilation. 

 They found that the pressure capable of being generated by the 

 saliva flowing from Wharton's duct might considerably surpass 



