270 HISTOLOGICAL CHANGES. [BOOK IT. 



the large quantity of mucigen to which it has given rise ; that 

 is to say, the growth of new protoplasm does not keep pace with 

 the manufacture of protoplasm into mucigen. During activity 

 the mucigen is used up to provide the mucus of the saliva, 

 being probably converted into mucin and so discharged from the 

 cell, while at the same time the protoplasm takes a fresh start and 

 grows apace ; and thus a fresh supply of new, deeply-staining 



Ctoplasm takes the place of the mucigenous matrix which has 

 n lost. We may remark incidentally that this rejuvenescence 

 of the protoplasm is marked as in the corresponding phase of the 

 pancreas, by the nucleus becoming round and conspicuous, whereas 

 when the mucigen is abundant it is of such a nature as to become 

 irregular in outline when acted upon by hardening reagents. 



We have reason to think that in certain cases, where the activity 

 of the cell is long-continued and vehement, the whole cell may 

 disappear, and its place be taken by an entirely new cell supplied 

 by the so-called demilune cells lying on the outside of the alveolus 

 beneath the basement membrane. But in ordinary cases the 

 same cell probably, for a while at all events, continues to form and 

 discharge successive quantities of mucin without actually itself 

 disappearing. 



In any case we see that in the mucous cell what takes place 

 in secretion is as follows. As the result of a period of rest there ac- 

 cumulates in the cell a quantity of mucigen, which is a product of 

 the metabolism of the protoplasm of the cell. During the active 

 phase, that is while the secretion is being poured forth, the 

 mucigen is converted into mucin and discharged from the cell. 

 A loss consequently accrues to the cell, but this is at once partly 

 made up by the protoplasm being stirred to a more active growth. 

 Subsequently during the succeeding rest the new protoplasm is 

 transformed into new mucigen, the cell wholly regains its former 

 dimensions and features and so the cycle is completed. 



What relation do these changes in the mucous gland bear to 

 those of the pancreas ? To answer this question we must bring 

 the reader back to a statement made on p. 255, that in order to 

 obtain an actively proteolytic aqueous pancreatic extract, the 

 animal should be killed during full digestion. This statement now 

 requires modification. 



If the pancreas of an animal, even in full digestion, be treated, 

 while still warm from the body, with glycerine, the glycerine 

 extract, as judged of by its action on fibrin in the presence of 

 sodium carbonate, is inert or nearly so as regards proteid bodies. 

 If, however, the same pancreas be kept for 24 hours before being 

 treated with glycerine, the glycerine extract readily digests fibrin 

 and other proteids in the presence of an alkali. If the pancreas, 

 while still warm, be rubbed up in a mortar for a few minutes 

 with dilute acetic acid, and then treated with glycerine, the 

 glycerine extract is strongly proteolytic. If the glycerine extract 



