1020 OP GENERATION. 



their size is very much reduced, and their extent greatly increased (Fig. 281). 

 These, like the reservoirs and mammillary tubes, are composed of a fibrous coat 

 lined by a mucous membrane ; the latter is highly vascular, and forms a secre- 

 tion of its own, which sometimes collects in considerable quantity when the milk 

 ceases to be produced. The smaller subdivisions of the lactiferous tubes pro- 

 ceed to distinct lobuli in each glandule ; so that when a branch of a mammary 

 tube has been filled with injection, its attached lobules, if separated from each 

 other by long maceration, are like a bunch of fruits clustered upon a stalk (Fig. 

 282). When the lactiferous tubes are pursued to their ultimate distribution, 

 they are found to terminate in follicles, whose size, in full lactation, is that of 

 a hole pricked in paper by the point of a very fine pin, so that when distended 

 with quicksilver or milk, they are just visible to the naked eye ; at other times, 

 however, the follicles do not admit of being injected, though the lactiferous 



Fig. 282. Fig. 283. 



Termination of portion of Milk- Ultimate follicles of Mammary 



duct in a cluster of follicles ; from Gland, with their secreting cells, 



a mercurial injection; enlarged four a, a; b, b, the nuclei. 



tubes may have been completely filled. They are lined by a continuation of the 

 same membrane with that which lines the ducts ; and this possesses a high vas- 

 cularity. The arteries which supply the glandules with blood become very 

 large during lactation ; and their divisions spread themselves minutely on the 

 follicles. From the blood which they convey, the milk is secreted and poured 

 into the follicles, whence it flows into the ducts. The inner surface of the milk- 

 follicles, in common with other glandular structures, is covered with a layer of 

 epithelium-cells (Fig. 283), as was first observed by Prof. Goodsir ; and these, 

 being seen to contain milk-globules, may without doubt be regarded as the real 

 agents in the secreting process. Absorbent vessels are seen to arise in large 

 numbers in the neighborhood of the follicles ; their function appears to be to 

 absorb the more watery part of the milk contained in the follicles and tubes, so 

 as to render it more nutrient than it is when first secreted ; and also to relieve 

 the distension which would occur, during the absence of the child, from the 

 continuance of the secreting process. The Mammary gland may be detected at an 

 early period of foetal existence ; being easily distinguishable from the surround- 

 ing parts by the redness of its color and its high vascularity, especially when 

 the whole is injected. At this period, it presents no difference in the male 

 and female ; and it is not until near the period of puberty that any striking 

 change manifests itself, the gland continuing to grow, in the one sex as in the 

 other, in proportion to the body at large. At about the age of thirteen years, 

 however, the enlargement of the gland commences in the Female \ and by six- 

 teen, it is greatly evolved, and some of the lactiferous tubes can be injected. 

 At about the age of twenty, the gland attains its full size previous to lactation ; 

 but the milk-follicles cannot even then be injected from the tubes. During 

 pregnancy, the mammae receive a greatly increased quantity of blood. This 

 determination often commences very early, and produces a feeling of tenderness 

 and distension, which is a valuable sign (where it exists in connection with 



