THE FEMALE REPRODUCTIVE ORGANS. 855 



the last menstruation. The actual time of delivery, however, 

 shows considerable variation. Delivery occurs in consequence of 

 contractions, more or less periodical, of the musculature of the 

 uterus, and reflex as well as voluntary contractions of the abdom- 

 inal muscles. It has been shown that delivery may occur when the 

 nerves connecting the uterus with the central nervous system are 

 severed, so that the act is essentially an independent function of 

 the uterus, although under normal conditions the contractions of 

 this organ are doubtless influenced by reflex effects through its 

 extrinsic nerves. It has been shown that contractions of the gravid 

 uterus may be caused by stimulation of various sensory nerves, and 

 in women it is known that delivery may be precipitated prematurely 

 by various mental or physical disturbances. The interesting prob- 

 lem physiologically is to determine the normal factor or factors that 

 bring on uterine contractions at term. Various more or less unsatis- 

 factory theories have been proposed. Some authors attribute 

 the act to a change in the maternal organism, such as mechani- 

 cal distension of the uterus, a venous condition of the blood, a 

 degenerative change in the placenta, etc., while others suppose that 

 the initial stimulus comes from the fetus. In the latter case it 

 is suggested that the increasing metabolism of the fetus is insuffi- 

 ciently provided for by the placental exchange, and that therefore 

 certain products are formed which serve to stimulate the uterus 

 to contraction. 



The duration of the labor pains is variable, but usually they are 

 longer in primiparse, ten to twenty hours or more, than in multip- 

 ara?. After the fetus is delivered the contractions of the uterus 

 continue until the placenta also is expelled as the " after-birth." 

 During these latter contractions the fetal blood in the placenta is, 

 for the most part, squeezed into the circulation of the new-born 

 child. The hemorrhage from the walls of the uterus due to the rup- 

 ture of the placenta may be profuse at first, but under normal con- 

 ditions is soon controlled by the firm contraction of the uterine walls. 



The Mammary Glands. At the time of puberty the mam- 

 mary glands increase in size, but this growth is confined mainly 

 to the connective tissue; the true glandular tissue remains rudi- 

 mentary and functionless. At the time of conception the gland- 

 ular tissue is in some way stimulated to growth. Secreting alveoli 

 are formed, and during the latter part of pregnancy they produce 

 an incomplete secretion, scanty in amount, known as colostrum. 

 After delivery the gland evidently is again brought under the 

 influence of special stimuli. It becomes rapidly enlarged and a 

 more abundant secretion is formed. For the first day or two 

 this secretion still has the characteristics of colostrum, but on 

 the third or fourth day the true milk is formed and thereafter is 



