348 TRYPSIN AND TRYPSINOGEN. [BOOK n. 



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

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

 juice secreted. In the fresh cell this material may generally be 

 recognized under the microscope by its optical characters as gran- 

 ules , 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 differ- 

 entiate 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 neces- 

 sary 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 gran- 

 ules, and that the formative activity should cease when the secre- 

 tory 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 unimals it would appear 

 that such a continued balancing of load and discharge does actu- 

 ally take place, so that no distinction in granules can be observed 

 between resting and active cells. 



200. 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 transparent material lodged in the spaces of the cell- 

 substance, which material even if not exactly identical with at 

 least closely resembles the mucin found in the secretion ; and ap- 

 parently, in the act of secretion the granules do undergo some 

 such change. In the case of some other glands moreover we 

 have chemical as well as optical evidence that the material stored 

 up in the cell is, in part at least, not the actual substance appear- 

 ing in the secretion but an antecedent of that substance. 



