34 MILK 



in the habit of manipulating and massaging his left gland during 

 his idle time, and this was the cause of milk secretion. Such 

 cases are rare, of course, and the secretion, though resembhng milk, 

 is more watery. 



The progressive stages in the development of the mammary- 

 gland are well summarized by Gaines in the following manner: 



"Embryonic Stage. — The first signs of mammary organs, the 

 milk line, appears at an early stage in embryonic life, and growth 

 is continued until the gland reaches a considerable development 

 at birth. 



"Birth. — At birth a milky fluid may be expressed from the 

 gland in either sex (the so-called witch's milk), indicating secretory 

 activity, but this activity soon ceases and the gland remains 

 quiescent until puberty. 



"Puberty. — At puberty, under the influence of the ovaries, 

 growth is resumed and carried to a greater or less development, 

 varying with the individual and the occurrence of pregnancy. 



"Pregnancy induces a great hypertrophy of the gland, and it 

 reaches a high state of development, accompanied by the accumu- 

 lation of colostrum. 



"Delivery. — By the time of delivery milk secretion proceeds 

 actively, and if the milk is removed at short intervals by nursing 

 or artificially secretion continues for a period of days, months, or 

 years. The rate of secretion, however, after a time gradually de- 

 creases to zero. This decrease is favored by a succeeding preg- 

 nancy. 



"Pregnancy. — Further growth of the gland ensues, but not as 

 marked as in the preceding gestation. 



"Delivery. — At dehvery milk secretion is again actively resumed. 

 Whence the pregnancy delivery cycle is repeated." 



The mammary gland of woman increases in size during preg- 

 nancy, especially during the second half of this period. This be- 

 comes manifest by an appearance of fulness and a feeUng of ten- 

 sion in the breasts. During growth the breast sinks, owing to 

 increased weight, and the veins become more prominent. In the 

 first pregnancy this increase is more pronounced than during suc- 

 ceeding ones. After lactation the gland is reduced, but never re- 

 turns to the original size. 



Formation of the Secretion 



The cells of the gland unload their contents into alveoh which 

 take part in the formation of the secretion, milk-fat in particular. 

 The fat is contained in the cells and the larger globules appear 

 at that part of the cell which points toward the lumen. When the 



