CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 413 



basement membrane, but no characteristic disappearance of gra- 

 nules can be observed. In the living state, the cell-substance of 

 these ovoid cells appears finely granular, but in hardened and 

 prepared sections has a coarsely granular, " reticulate " look which 

 is perhaps less marked in the swollen active cells than in the 

 resting cells. 



237. All these various secreting cells then, pancreatic cell, 

 mucous cell, albuminous cell, and central gastric cell, exhibit the 

 same series of events, modified to a certain extent in the several 

 cases. In each case the 'protoplasmic' cell-substance manufactures 

 and lodges in itself material destined to form part of the juice 

 secreted. In the fresh cell this material may generally be recog- 

 nized under the microscope by its optical characters as granules ; 

 these however are apt to become altered by reagents. But we must 

 guard ourselves against the assumption that the material which can 

 thus be recognized is the only material thus stored up ; we may, 

 in future, by chemical or other means be able to differentiate other 

 parts of the cell-body as being also material similarly stored up. 



During activity, while the gland is secreting, this material, 

 either unchanged or after undergoing change, is wholly or partially 

 discharged from the cell. The cell in consequence of having thus 

 got rid of more or less of its load consists to a larger extent of 

 actual living cell-substance, this being in many cases increased by 

 rapid new growth, though the bulk of the discharged cell may be 

 less than that of the loaded cell. 



This activity of growth continues after the act of secretion, but 

 the discharged cell soon begins again the task of loading itself 

 with new secretion material for the next act of secretion. 



Thus in most cases there is, corresponding to the intermittence 

 of secretion, an alternation of discharge and loading ; but it must 

 be borne in mind that such an alternation is not absolutely necessary 

 even in the case of intermittent secretion. We can easily imagine 

 that the discharge, say, of ' granules ' during secretion should stir 

 up the cell to an increased activity in forming granules, and that 

 the formative activity should cease when the secretory activity 

 ceased. In such a case the number of new granules formed might 

 always be equal to the number of old granules used up, and the 

 active cell in spite of its discharge would possess as many granules, 

 that is to say, as large a load, as the cell at rest. And in the central 

 gastric cells of some animals it would appear that such a continued 

 balancing of load and discharge does actually take place, so that no 

 distinction in granules can be observed between resting and active 

 cells. 



238. We spoke just now of the material stored up in the 

 cell and destined to form part of the secretion as undergoing change 

 before it was discharged. In the mucous cell we have seen that 

 the material deposited in the living cell has at first the form of 

 granules. These granules however are easily converted into a 



