PHT8I0L001 OP THE DIGE8TTV1 OLANDE ll!l 



the permeability of the lumen border of the eelL Thia change in permea- 

 bility may be dependent upon alterations in surface tension brought 

 about by the migration of electrolytes to the border. That such a migra- 

 tion of electrolytes docs actually occur has been den by A B 

 Macallum 8 who developed a microchemical tesl for potassium, by the use 

 of which he was able to show thai this electrolyte accumulates at the lumen 



border of il II during secretory activity, that is. al the border of the 



cell through which the secretion takes place. Potassium may be taken 

 as a prototype of electrolytes in general. In the epithelium of the -mall 

 intestine, where the currenl goes in the opposite direction to thai in 

 gland cells, the accumulation of potassium occurs al the portion of the 

 cell next the basement membrane. 



Other observers believe that, when the gland becomes more active, the 

 molecules present in the cell become broken down into smaller mole.- 

 and so raise the osmotic pressure of the cell content, with the result that 

 water is attracted from the blond and is then transferred to the lumen. 

 When the gland is excited so that the zymogen granules, aa well as 

 water and salts, are secreted, the primary change appears to involve the 

 granules only. Those near the lumen swell up by absorbing \ and 



become converted into spheres in which salts are dissolved in smaller 

 proportions than exist in the lymph bathing the cells. These swollen 

 structures are then ruptured a1 the periphery of the cell and discharged 

 into the lumen. This discharge of a fluid containing fewer saline con- 

 stituents than the cell or surrounding blood plasma brings about in- 

 creased concentration in the remaining parts of the cell, a p which 

 possibly is assisted by a breaking up of molecules In the protoplasm itself, 

 and which causes an increase in osmotic pressure with a conseqn 

 How of water from the lymph to the cells and therefore from the bl 

 to the lymph. 



OTHER CHANGES DURING ACTIVITY 



Whatever may be the nature of the physiological changes thai 

 are responsible for the secretory activity of the cell, the fact star 

 prominently that a considerable expenditure of energy is entailed T 

 is indicated by the fad thai considerably larger quantity 

 are taken up by the gland when it is in an active state than whei 

 rest. Thus, the oxygen consumption of the resting submaxillary gland 

 of the cat may be increased five times during active tion. 



account of this increased oxygen consumption it is i rprising that 



it should be found that the Becretory activity of tin 11 ; ~ im- 



paired by a deficiency in oxygen. 



