210 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



columnar epithelium with the nuclei situated at the 

 base of the cells near the basement membrane. 

 These are the chief cells of the alveoli and they se- 

 crete mucus, which is first stored up in the cyto- 

 plasm in coarse granules 

 known as mucigen. A 

 second form of cells, less 

 numerous, is found singly 

 or in groups in the periph- 

 ery of the alveoli and in 

 close apposition to the 

 basement membrane. 

 On account of their shape 

 and position they are 

 called parietal cells, cres- 

 cents of Gianuzzi, or demi- 

 lunes of Heidenhain. 

 They are finely granular, 

 stain red with eosin, and 

 are looked upon by some 

 as secreting a serous fluid. 

 There are three theories 

 as to their use : (i) They 

 may be considered as 

 worn-out chief cells that 



have been crowded to the basement membrane after 

 too active a secretion. (2) They may be considered 

 as latent undeveloped cells ready to take the place 

 of mucous cells that get lost in the process of active 

 secretion. (3) They may be considered as normal 

 active cells contributing constantly to the salivary 

 secretion in a way that is at present unknown. 



Fig. 156. Model of a small 

 portion of a sublingual gland of 

 man. The demilunes of Heid- 

 enhain are more deeply shaded 

 (Maziarski, " AnatomischeHefte," 

 1901). 



