Joseph Marshall Flint 289 



width of two alveoli. Sometimes they may approach as near as one 

 alveolus but an instance of a duct lying adjacent to the limiting mem- 

 brane is almost impossible to find, except at the hilus, where the lobular 

 duct enters the lobule. Once in the lobule the duct loses its double 

 layer of epithelium and is lined from this point with a single layer of 

 short columnar or cubical cells which are characteristic of the ducts in 

 this region. These intralobular ducts are known throughout the liter- 

 ature as the " salivary tubes of Pfluger " who believed that they were 

 concerned in the metabolic activities of the gland and took an active 

 part in the phenomena of secretion. These cells have oval or vesicular 

 nuclei which are situated about the center of the cells. As a rule they 

 take the stain somewhat more deeply than the nuclei of the epithelium 

 in the extralobular ducts. The portion of the cell towards the lumen 

 of the duct is composed of granular cytoplasm which stains deeply with 

 the ordinary acid contrast dyes, such as congo red, eosin, or the picric 

 acid element of the Van Gieson stain. The pole of the cell external to 

 the nucleus shows a characteristic appearance of longitudinal striations 

 which run from the central portion just below the nucleus to the end 

 of the cell near the basement membrane. In cells that have been iso- 

 lated from the ducts the portion of the cytoplasm occupied by these 

 striations splits into little staves which often spread out much like the 

 sticks of a fan. Protoplasmic bridges have been described running be- 

 tween the individual filaments composing these striations. 



As we have seen from the corrosions, the intercalary ducts form the 

 termination of the intralobular ducts and connect them with the alveoli. 

 They are seen readily in sections where they appear when undistended 

 only about one-third of the diameter of the intralobular ducts. The 

 epithelium of these structures changes suddenly from the striated cubi- 

 cal cells and is composed of rather long, flattened epithelium cells 

 with their major axis running parallel to the axis of the duct. The 

 nuclei are elongated, less deeply staining than the nuclei of the cells 

 in ducts of the next lower order. The cytoplasm is neither so 

 rich in quantity nor does it have the same affinity for the acid dyes 

 that Ave have observed in the cells of' the intralobular ducts. The 

 boundaries of the cells, mxOreover. are somewhat obscured. When cut 

 in cross-section the lining cells of these ducts appear as flattened cu- 

 boidal epithelial elements. There is little elastic tissue about either the 

 •lobular or intralol)ular or intercalary ducts, only an occasional fibril can 

 be marie out surrounding them. The regular elastic membranes des- 

 cribed in the extralobular system cease shortly after the ducts become 

 intralobular. Sometimes, however, they may Ite observed following the 



