326 MATHEWS. 



the inner end of the cell, and the secretion be expelled from the 

 cell by intra-cellular tension, and from the ducts by the elastic 

 tension of the distended alveolar wall. Or, second, it must be 

 assumed that, as the fluid flows from the cell, new fluid enters 

 the cell from the rear, so that the cell does not diminish in bulk 

 to an extent aqual to the bulk of secretion it has lost. Either 

 of these assumptions lands us at once in difficulties. If the first 

 be true we cannot understand why the sympathetic secretion 

 should be abnormally large, just in those cases, such as par- 

 alytic secretions, or after long-continued chorda secretion, in 

 which the alveoli are not distended and are not presumably 

 under pressure. The second assumption, besides being wholly 

 imaginary, has to explain whence comes the fluid flowing into 

 the cell, and why it should flow in during sympathetic stimu- 

 lation at a time when there is a pronounced vaso-constriction. 

 With this difficulty of understanding how the nerve could cause 

 a secretion by action on the cell, let us see how the sudden back 

 flow could be understood. According to von Wittich and 

 Heidenhain the diameter of the alveoli has remained constant. 

 The secretion, manifestly, cannot upon this assumption return 

 into the gland, unless there be a diminution in the combined 

 bulk of the secretion in the ducts and the cells. There will be 

 no such alteration in bulk, however, by the secretion passing into 

 the cell as von Wittich assumes, for the cell will grow to just 

 the amount that the secretion in the lumen diminishes. The 

 only way a diminution in bulk could be brought about is by a 

 back filtration. The fall is, however, much too sudden for this, 

 and takes place at a pressure much less than the gland can sus- 

 tain without becoming cedematous. It is also impossible to see 

 why on ceasing stimulation the permeability of the gland to back 

 filtration should suddenly increase. Easy though it seems at 

 first sight, therefore, to ascribe such a back flow to a reabsorp- 

 tion under pressure of saliva by the cell, closer inquiry shows 

 that it is impossible to account for this back flow except on the 

 assumption either of a back filtration or that there has been an 

 alteration in the diameter of the alveoli. I maintain with Eck- 

 hard that a back filtration is highly improbable, and there re- 



