THE FEMALE REPRODUCTIVE ORGANS 



543 



The Active Gland. During lactation the glandular alveoli are so 

 numerous as to form by far the most prominent portion of the gland. 

 Each lobule consists of a cluster of saccular alveoli which open by short 

 alveolar ducts into the interlobular ducts of the connective tissue which 

 invests the lobules of the gland. The alveoli are closely packed within 

 the lobule. 



The actively secreting alveoli are lined by cuboidal or low columnar 

 cells which vary much in height even within the same alveolus, and are 

 often considerably flattened. Fat drop- 

 lets accumulate within the distal portion 

 of their cytoplasm. The droplets in- 

 crease, in size as well as in number, 

 until they finally occupy the greater 

 part of the distal end of the cell and 

 are separated from each other by only 

 a narrow interval of albuminous cyto- 

 plasm. Finally the fat droplets are 

 discharged into the broad lumen of the 

 alveolus, where they apparently still re- 

 tain a thin albuminous envelope which 

 prevents their cohesion and consequent 

 fusion, and thus permits their suspen- 

 sion in the albuminous, fluid portion of 

 the milk. The milk may include also 

 cytoplasmic and nuclear debris. 



The spherical nuclei of the secret- 

 ing cells during this process are crowd- 

 ed to the base of the cell, and after the discharge of the secretion the 

 shrunken but nucleated cell remnants remain in situ; after a period 

 of rest the cells apparently resume their secretory function. It appears 

 probable that each cell in its life history may repeatedly pass through 

 the cycle of secretory changes, though the exact number of such cycles 

 which an individual cell may present obviously does not admit of dem- 

 onstration. 



As a rule, the active epithelium consists of a single row of cells, 

 though here and there they appear as if piled upon one another to form 

 a double layer. During pregnancy many of these cells may be seen in 

 mitosis. The actively secreting cells contain basal (ergastoplasmic) fila- 

 ments. According to Hoven (Anat. Anz., 39, 1911) these filaments 

 break up into granules from which minute fat spherules develop. The 



FIG. 475. MODEL OF A RECON- 

 STRUCTION OF AN INTRALOB- 

 ULAR DUCT AND ITS ACINI 

 FROM THE ACTIVE MAMMARY 

 GLAND OF A WOMAN. 



X 200. (After Maziarski.) 



