STRUCTURE AND SECRETORY ACTIVITY OF MAMMARY GLANDS. 417 



STRUCTURE AND SECRETORY ACTIVITY OF THE MAMMARY 



GLANDS. 



About twenty milk-ducts open separately on the tip of the nipple, and just 

 in advance of their mouth present an oval dilation, the lacteal sinus, generally ex- 

 panded laterally. Each undergoes dendritic ramification and passes to a spe- 

 cial lobe of the gland, which is bound together by loose interstitial connective 

 tissue. Only at the time of lactation do all of the terminal branches of the milk- 

 ducts lead to round glandular acini arranged in groups. Each vesicle has a 

 membrana propria, upon which externally is a network of star-shaped connective- 

 tissue cells, and internally a single layer of somewhat flattened, polyhedral and 

 nucleated secretory cells. According to the degree of secretory activity of the 

 acinus its lumen, at times narrow, at other times wide, is filled with a fluid in 

 which float round, shining fat-granules (milk). Fibrillary connective tissue, 

 principally arranged in a circular manner, and transversed externally by fine 

 elastic fibers, forms the wall of the glandular ducts, which are lined by cylindrical 

 epithelium. In the smallest of these a membrana propria can yet be recognized, 

 which is continuous with that of the terminal vesicle. 



During the first days following delivery (as well as before it), the breasts 

 secrete little milk of considerable consistency and yellowish color (colostrum) , in 

 which large cells completely filled with fat-granules are present (colostrum-corpus- 

 cles). The latter appear also later on, when the discharge of the milk has for 

 a time been discontinued. Sometimes a nucleus is recognizable in the cells, 



FIG. 137. /, Acinus of the mammary gland, inactive; II, during the formation of milk: a, b, milk-globules; 

 c d e, colostrum-corpuscles; /, pale cells (from the dog). 



rarely ameboid movement (Fig. 137, c, d, e). The normal secretion of milk, 

 appearing in the course of three or four days, is a productive activity of the gland- 

 cells. 



Heidenhain and Partsch found the secretory cells in the inactive gland (Fig. 

 137, 7) to be flat, polyhedral and mononuclear; on the other hand, in the active 

 gland often polynuclear, cylindrical, higher, and richer in albumin and granules 

 (Fig. 137, //). The free edge, turned toward the cavity of the acinus, undergoes 

 characteristic changes during secretion. There are formed in this part of the 

 cells fat-granules, which are thrown off during secretion, together with the de- 

 tached cell-margin. In part the nuclei also, degenerate, their product likewise 

 passing over into the milk (nuclein-content of milk). The same cells appear 

 to be able to perform the secretory process repeatedly, undergoing regeneration 

 during the period of rest. According to Bizzozero, Benda, Michaelis and Unger, 

 the cells actively produce the fat-granules and throw them off. 



Leukocytes containing fat-granules are, further, found in milk, representing 

 colostrum-corpuscles, and isolated, pale cells (/). Some' milk-globules still have 

 shreds of cell-substance on their surface (6) . With respect to the formation of the 

 individual constituents of milk, H. Thierfelder, who exposed fresh mammary 



t lands to digestive processes immediately after death, found that during the 

 igestion of the gland at the temperature of the body a reducing substance, 

 probably milk-sugar, was formed as a result of fermentative activity. The 

 mother-substance (saccharogen) is soluble in water, but not in alcohol or ether; 

 it is not destroyed by boiling and is not identical with glycogen. The ferment 

 forming milk-sugar seems to be fixed in the glandular cell, as it does not pass 

 over into the milk or into a watery extract of the gland. During the digestion 

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