594 



PHYSIOLOGY OF GONADS 



even when immature, is three-dimensional 

 demand other methods. For such cases a pre- 

 cise but rather tedious method has been 

 described by Benson, Cowie, Cox and Goldz- 

 veig (1957) which involves the determina- 

 tion of the volume of glandular tissue from 

 area measurements of serial sections of the 

 gland in conjunction with semiquantitative 

 scoring procedures for assessing the mor- 

 phologic characteristics of the tissue. 



Particularly applicable to the lactating 

 gland is the procedure developed by Rich- 

 ardson (see Cowie, Folley, Malpress and 

 Richardson, 1952; Richardson, 1953) for as- 

 sessing the total internal surface area of the 

 mammary alveoli. It is of interest to note 

 in passing that this technique is based on 

 that developed by Short (1950) for measur- 

 ing the surface area of the alveoli in the 

 lung, the similarity in the geometry of the 

 two organs allowing ready transference of 

 the method from one to the other. 



At present these quantitative procedures 

 have the disadvantage of being slow and 

 time consuming, and it seems likely that 

 their further development will involve the 

 use of electronic scanning methods to speed 

 up the examination of the tissues. Of recent 

 introduction are some biochemical proce- 

 dures for assessing changes in mammary 

 development. The desoxyribonucleic acid 

 (DNA) content of any particular type of 

 cell is said to be remarkably constant (see 

 Vendrely, 1955, for review) and the amount 

 of DNA in a tissue has been used as a refer- 

 ence standard directly related to the number 

 of cells present in a tissue and to provide an 

 estimate of the number of cells formed dur- 

 ing the developmental phases of a gland or 

 tissue (see Leslie, 1955, for review). Studies 

 on DNA changes which occur in the mam- 

 mary gland during pregnancy and lactation 

 have been made in the rat by Kirkham and 

 Turner (1953), Grecnbaum and Slater 

 (1957a), Griffith and Turner (1957), and 

 Shimizu (1957). It should be noted, how- 

 ever, that some authorities have doubts as 

 to the constancy under all conditions of the 

 DNA content of a cell (see Brachet, 1957) 

 and results obtained by this technique 

 should be interpreted with some caution 

 (see also Griffith and Turner, 1957). Other 

 chemical methods for assessing mammary 

 development include (a) the determination 



of the iron content of the gland, based on 

 the observation that iron retention occurs in 

 the epithelium of the mammary glands of 

 mice (Rawlinson and Pierce, 1950) ; (b) 

 whole-mount autoradiographs using P^- 

 (Lundahl, Meites and Wolterink, 1950) ; 

 and (c) determination of the total content 

 of alkaline phosphatase in the mammary 

 gland (Huggins and Mainzer, 1957, 1958). 



In view of the relative rapidity of the bio- 

 chemical methods it seems likely that they 

 will be used increasingly in the future. 



A technique of clinical interest allowing 

 the qualitative assessment of changes in 

 mammary structure in the breast of preg- 

 nant and lactating women is the radio- 

 graphic method described by Ingleby, Moore 

 and Gershon-Cohen (1957). 



To those seeking information of the mi- 

 croscopic anatomy of the human mammary 

 gland we would recommend the excellent 

 and beautifully illustrated review by Dabe- 

 low (1957), and new facts on the cyto- 

 logic changes occurring during milk secre- 

 tion will be found in the electron microscopic 

 study of the rat mammary gland by Barg- 

 mann and Knoop (1959), and of the mouse 

 mammary gland by Hollmann (1959). 



Having briefly outlined the various quan- 

 titative methods of assessing mammary de- 

 velopment we will now consider recent 

 studies on normal mammary growth. 



2. Mammary Development in the X on preg- 

 nant Female 



It has been the general belief that until 

 puberty the mammary ducts show little 

 growth, but more precise studies in which 

 the rate of increase in mammary gland area 

 has been related to the increase in body size 

 have now shown that in the monkey, rat, 

 and mouse a phase of ra])id duct growth is 

 initiated before puberty. 



The first use of this procrdure, relative 

 gi'owth analysis (for terminology see Hux- 

 ley and Teissier, 1936), for the quantitative 

 investigation of mammary duct growth was 

 made by Folley, Guthkelch and Zuckerman 

 (1939), who showed that over a wide range 

 of body weights, the breast in the nonpreg- 

 nant female rhesus monkey grows faster 

 than the body as a whole. Subsequently, 

 more detailed studies of the dynamics of 

 mammary growth using relative growth 



