676 



PHYSIOLOGY OF DIGESTION AND SECRETION. 



Fig. 258. Mucous gland: submaxillary of dog; rest- 

 ing stage. 



In the cells of the mucous glands changes equally marked may be 

 observed after prolonged activity. In stained sections of the resting 

 gland the cells are large and clear (Fig. 258), with flattened nuclei 

 placed well toward the base of the cell. When the gland is made to 

 secrete the nuclei become more spherical and lie more toward the 



middle of the cell, and 

 the cells themselves be- 

 come distinctly smaller. 

 After prolonged secretion 

 the changes become more 

 marked (Fig. 259) and, 

 according to Heidenhain, 

 some of the mucous cells 

 may break down com r 

 pletely. According to 

 most of the later observ- 

 ers, however, the mucous 

 cells do not actually dis- 

 integrate, but form again 

 new material during the 

 period of rest, as in the 

 case of the goblet cells of the intestine. In the mucous as in the 

 albuminous cells observations upon pieces of the fresh gland seem 

 to give more reliable results than those upon preserved specimens. 

 Langley* has shown that in the fresh mucous cells of the submax- 

 illary gland numerous large granules may be discovered, about 125 

 to 250 to a cell. These 

 granules are comparable to 

 those found in the goblet 

 cells, and may be inter- 

 preted as consisting of mu- 

 cin or some preparatory 

 material from which mucin 

 is formed. The granules 

 are sensitive to reagents; 

 addition of water causes 

 them to swell up and dis- 

 appear. It may be as- 

 sumed that this happens 

 during secretion, the gran- 

 ules becoming converted to a mucin mass which is extruded from 

 the cell. 



Action of Atropin, Pilocarpin, and Nicotin upon the Secre- 

 tory Nerves. The action of drugs upon the salivary glands and 

 "Journal of Physiology," 10, 433, 1889. 



Fig. 259. Mucous gland: submaxillary of 

 dog after eight hours' stimulation of the chorda 

 tympani. 



