152 MANUFACTURING CELLS 



Now during activity he found that there was the densest con- 

 densation of potassium at (3), the cell-lumen interface, less 

 potassium was found at the cell-cell interface and least at (1), the 

 cell-lymph interface. According to the Gibbs-Thompson principle 

 these results may be taken as an indication. 



(a) That during rest there is no marked difference of surface 

 tension at the gland interfaces, and 



(b) That during activity a high tension develops at the surface 

 between cell and lymph, a low tension between cell and lumen 

 and that the cell-cell interface has a value intermediate. 



4. It is well known that during glandular activity there is an 

 increase in the rate at which blood enters the gland. In other 

 words raw material and power are taken into the factory at an 

 increased rate. The view was at one time held that the secretion 

 was due to this increased flow of blood. Barcroft's experiments 

 have shown that this cannot be true, because 



(a) The increase in the blood flow through the organ is initiated 

 after the secretion begins and is continued for some time after 

 secretion has ceased ; and 



(b) Vaso-dilatation may take place without secretion. 



The increase in blood flow or vasodilatation is a consequence 

 of secretion and not the secretion a result of the vasodilatation. 

 The actively secreting gland, as it were, sends out a call for 

 oxygen, for power and for material. This call is in part met 

 by this increase in the transport service (see Chap. XXIV.). 



5. Alterations take place in electrical potential of one part of 

 the gland to another. These have been studied principally by 

 Bayliss and Bradford on the salivary gland and by Orbelli on 

 the skin glands of the frog. The results vary somewhat with 

 the means of investigation, but may be taken as indicating two 

 things. 



(a) The secretion of water, i.e. dispatch of secretion, is a different 

 function of the gland or a function of a different mechanism in 

 the gland from the elaboration of the true secretory material. 

 That is, we have to consider two phenomena, the preparation of 

 material and its flooding out of the cell by water. The former is 

 accompanied by 



(b) A large difference of potential between the cell-lymph 

 interface and the cell-lumen interface, the latter by a small 

 potential difference of the opposite sign from the former. 



The cause of the former difference may be sought in the in- 

 creased permeability (lowered surface tension) of the cell-lumen 



