ORGANS OF THE BODY. 



553 



tinue to present the same structure as before. The female breast is, how- 

 ever, at this period in a more perfect state than the male. 



At the commencement of puberty the formation of a considerable 

 number of gland-vesicles takes place in the female breast, and with tolerable 

 rapidity, causing the organ to assume its well-known shape. But even 

 still, and throughout the whole term of virginity, the gland does not attain 



541. The mammary gland from a 

 mature foetus, after Longer, a, central 

 knobbed mass with smaller internal I 

 and c, larger external buds. 



Fig. 542. Degenerated mammary gland 

 from woman 90 years of age. 



anything like its full development, for which the supervention of the 

 first pregnancy is requisite. In this state of maturity it remains through- 

 out the whole period of fecundity, decreasing, however in size when at 

 rest, and losing some of its vesicles. Finally, with the decline of the 

 reproductive powers a retrograde development of the mammary gland 

 takes place, with gradual disappearance of all its terminal vesicles, and 

 destruction of the smaller ducts, until eventually nothing but fatty tissue 

 is to be found in its place. It is represented in this condition in fig. 

 542. Here the canals only are to be found; everything else has dis- 

 appeared. The interstitial connective-tissue appears rich in elastic fibres 

 (Langer). 



The mammary gland of the male (fig. 539, 6), with very rare exceptions, 

 never attains the same degree of development as in the female. In it we 

 generally find nothing but a system of ducts, varying greatly in size, no 

 trace of terminal secreting vesicles being apparent (Langer). 



282. 



Milk is an opaque bluish or yellowish -white fluid, without odour, 

 sweetish to the>taste, with a slightly alkaline reaction, and a sp. gr. usually 

 of about 1 -028-1 '034. When kept in a state of rest it separates into two 

 strata- an upper, thick, fatty, and white (cream) ; and a lower of much 

 thinner consistence. Some considerable time after this a process is set up, 

 in which its alkaline reaction is changed for an acid by the conversion of 

 sugar of milk into lactic acid. ' As a consequence of this, the casein con- 

 tained in the fluid coagulates, a change which is also effected by contact 

 with the mucous membrane of the stomach (p. 17). 



Anatomically, milk consists of a transparent fluid, in which innumer- 

 able fatty globules are suspended : it is therefore an emulsion. 



