MAMMARY GLAXD AND LACTATION 



595 



olO. 



rCMALC RATS 



ACt$ : i - lOO DAYS 



C 22 NO DAY 



LOC„ CBOOY WtlCHT C> 



Fig. 10.2. Relative mammary gland growth in the female hooded Norway 

 Cowie. J. Endocrinol.. 6, 145-157, 1949.) 



(From A.T. 



analysis were made in the rat by Cowie 

 (1949) and Silver (1953a, b) and in the 

 mouse by Flux (1954a, b), and their results 

 will now be summarized. In the rat the 

 total mammary area increased isometrically 

 with the body surface (a = 1.1 as compared 

 with the theoretic value of 1.0) until the 

 21st to 23rd day when a phase of allometry 

 (a = 3.0) set in. The onset of the allometric 

 phase could be prevented by ovariectomy on 

 the 22nd day (see Fig. 10.2). Since estrous 

 cycles do not begin until the 35th to 42nd 

 day in this strain of rat, it is clear that the 

 rapid extension of the mammary ducts be- 

 gan well before puberty. In the immature 

 male rat the increase of mammary area on 

 body surface was slightly but significantly 

 allometric; this was not altered by castra- 

 tion at the 22nd day. Earlier ovariectomy, 

 i.e., when the pups were 10 days old, was 

 followed by a phase of slightly allometric 

 growth of the mammary glands in the fe- 



males (a = 1.5). With regard to the female 

 mouse (CHI strain) a i)hase of marked al- 

 lometry in mammary duct growth set in 

 about the 24th day (a = 5.2) which could 

 also be prevented by prior ovariectomy. 



It is clear that the presence of the ovary 

 is essential for the change from isometry to 

 allometry, but the nature of the mechanisms 

 governing the change is still uncertain (for 

 further discussion, see Folley, 1956). 



3. Mammary Growth in the Male 



The testes have apparently little effect on 

 mammary duct extension in the rat inas- 

 much as the gland in the male grows iso- 

 metrically or nearly so and its specific 

 growth rate is unaffected by castration. Cas- 

 tration at 21 days, however, does prevent 

 for a time development of the lobules of al- 

 veoli, first described by Turner and Schultze 

 (1931 ) , which are characteristic of the mam- 

 mary gland in the male rat. Eventually. 



