84 INTRODUCTION TO SEXUAL PHYSIOLOGY 



As mentioned already, a woman does not secrete true milk 

 until the second or third day after parturition. It is produced 

 at that time even though suckling does not take place, as when 

 the child has been born dead. It is necessary, however, in 

 man as well as in animals that the milk should be drawn off in 

 order to maintain the supply, and as is well known, a cow that 

 is not either sucked or milked soon runs dry. The quantity of 

 milk secreted by a woman at first undergoes some increase in 

 accordance with the needs of the child, but after about the 

 twenty-eighth week it begins to fall off, and after about a year 

 the supply ceases. Any longer period involves what is known as 

 hyperlactation, a practice which is generally deprecated in the 

 interests of the infant. Menstruation not infrequently com- 

 mences to occur during the lactation period (according to Fordyce 

 in 40 per cent, cases), and the latter may overlap gestation until 

 within a short time of delivery. The same is true approximately 

 also for the cow, in which animal, in the absence of a new 

 pregnancy, lactation may extend over a very long time. 



After the end of lactation the mammary glands gradually 

 return to the size they possessed before gestation, but not to 

 their prepuberal size. The cells lining the alveoli become 

 vacuolated and reduced in number, and as the process of involu- 

 tion proceeds many of the alveoli themselves disappear after 

 first becoming functionless. 



In the lower mammals (bitches, etc.) a fluid having all the 

 essential ingredients of milk is secreted some time after the oestrous 

 periods, even in virgins, provided that the mammary tissue 

 is sufficiently built up to admit of its functional activity. This 

 phenomenon, however, only appears to occur normally in animals 

 which ovulate spontaneously, so that corpora lutea " spuria " 

 can be formed, for, as will be shown in the next chapter, mammary 

 growth is mainly dependent upon the functional activity of the 

 corpus luteum. This organ is believed to be an essential factor 

 in the hypertrophy of the glands, but it undergoes involution in 

 the last part of pregnancy, and after parturition the anabolic 

 (or building up) processes no longer predominate in the mammary 

 tissue, the cells of the secretory alveoli undergoing catabolic 

 (or breaking down) changes, which manifest themselves in the 

 active production of milk. Mammary secretion may continue 

 for very prolonged periods after the removal of the ovaries, and 



