824 MATHEWS. 



exerted a secretory effect upon the gland, he considered the 

 secretion to be due to Jacobson's nerve alone. He concluded, 

 therefore, that stimulation of the sympathetic enormously in- 

 creased the content of organic solids in the cerebral saliva. The 

 sympathetic must hence act on the gland cells so as to render 

 their contents far more soluble. From Langley's results, how- 

 ever, we can safely conclude that the saliva, secreted when both 

 nerves are stimulated, is not pure cerebral saliva, but largely, if 

 not wholly, augmented sympathetic saliva. Like all sympa- 

 thetic saliva, it is more concentrated than the saliva secreted 

 under the influence of the dilator nerve, because it is expelled 

 without dilution. 



f. Other Evidenxe of the Muscular Nature of the 

 Mechanism of Sympathetic Secretion. 



Very clear evidence, also, has been brought forward by Eck- 

 hard,^^ von Wittich" and Heidenhain^^ himself that the sympa- 

 thetic causes at least the major part of its secretion, by a com- 

 pression of the ducts and alveoli. The parotid gland of the 

 sheep is an albuminous gland, capable of secreting against a 

 pressure of 400-500 m. m. of water (Eckhard). If while secret- 

 ing against a somewhat lower pressure (200-300 mm.) the 

 cervical sympathetic be stimulated, the water rises suddenly in 

 the manometer for some distance (30-100 mm.). On ceasing 

 stiimdation the secretion riisiies back at once into the gland nearly^ 

 tJioiigh never quite, to its former level. The higher the pressure 

 the more sudden the flow backward. The quick rise at the 

 beginning of stimulation and the abrupt back flow of the secretion 

 at the end plainly suggest that the nerve caused compression 

 of the ducts and alveoli, and thus pressed out the secretion. 

 On ceasing stimulation these structures dilated, and the secre- 

 tion, being under pressure, rushed back into the gland. I see 

 no other explanation for the back flow, as it takes place too 

 suddenly and at too low a pressure (200 mm. water) to be due 

 to back filtration. 



Heidenhain's observation is less striking, but it is similar to 



