STRUCTURE OF THE MAMMA. 463 



of milk, H. Thierfelder, who digested fresh mammary glands directly after death, 

 found that during the digestion of the glands at the temperature of the body, a 

 reducing substance, probably lactose, was formed by a process of fermentation. 

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

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

 forms the lactose is connected with the gland-cells it does not pass into the 

 milk, nor into a watery extract of the gland. During the digestion of the mammary 

 glands, at the temperature of the body, casein is formed, probably from serum- 

 albumin, by a process of fermentation. This ferment occurs in the milk. 



The nipple and its areola are characterised by the presence of pigment more 

 abundant during pregnancy in the rete Malpighii of the skin, and by large papillae 

 in the cutis vera. Some of the papillae contain touch-corpuscles. Numerous non- 

 striped muscular fibres surround the milk-ducts in the deep layers of the skin and 

 in the subcutaneous tissue, which contains no fat. These muscular fibres can be 

 traced following a longitudinal course to the termination of the ducts on the surface. 

 The small glands of Montgomery, which occur on the areola during lactation, are 

 small milk-glands, each with a special duct opening on the surface of the elevation. 



Arteries proceed from several sources to supply the mamma, but their branches 

 do not accompany the milk-ducts ; the gland acini are each surrounded by a net- 

 work of capillaries, which communicate with those of adjoining acini by small 

 arteries and veins. The veins of the areola are arranged in a circle (circulus 

 Halleri). The nerves are derived from the supraclavicular, and the II-IV-VI 

 intercostals ; they proceed to the skin over the gland, to the very sensitive nipple, 

 to the blood-vessels and non-striped muscle of the nipple, and to the gland acini, 

 where their mode of termination is still unknown. Lymphatics surround the 

 alveoli, and they are often full. The milk appears to be prepared from the lymph 

 contained in the lymphatics surrounding the acini. 



The comparative anatomy of the mamma. The rodents, insectivora, and car- 

 nivora, have 10 to 12 teats, while some of them have only 4. The pachydermata and 

 rurninantia have 2-4 abdominal teats, the whale has 2 near the vulva. The apes, 

 bats, vegetable-feeding whales, elephants, and sloths have 2, like man. In the 

 marsupials the tubes are arranged in groups, which open on a patch of skin devoid 

 of hair without any nipple. The young animals remain within the mother's pouch, 

 and the milk is expelled into their mouths by the action of a muscle the com- 

 pressor mammae. 



The development of the human mamma begins in both sexes during the third 

 month ; at the fourth and fifth months, a few simple tubular gland-ducts are 

 arranged radially around the position of the future nipple, which is devoid of hair. 

 In the new-born child the ducts are branched twice or thrice, and are provided 

 with dilated extremities, the future acini. Up to the 12th year in both sexes, the 

 ducts continue to divide dendritically, but without any proper acini being formed. 



In the girl at puberty the ducts branch rapidly ; but the acini are formed only at 

 the periphery of the gland, while during pregnancy, acini are also formed in the 

 centre of the gland, while the connective-tissue at the same time becomes some- 

 what more opened out. At the climacteric period, or menopause, all the acini and 

 numerous fine milk-ducts degenerate. In the adult male, the gland remains 

 in the non-developed infantile condition. Accessory or supernumerary glands 

 upon the breast and abdomen are not uncommon, sometimes the mamma occurs in 

 the axilla, on the back, over the acromion process, or on the leg. A slight secre- 

 tion of milk in a newly -born infant is normal. 



During the evacuation of the milk (500-1500 cubic centimetres daily), there is 

 not only the mechanical action of sucking, but also the activity of the gland itself. 

 This consists in the erection of the nipple, whereby its non-striped muscular fibres 

 compress the sinuses on the milk-ducts, and empty them, so that the milk may flow 

 out in streams. The gland acini are also excited to secretion reflexly by the stim- 



