DISEASES OF THE MAMMARY GLANDS. 



In mammalia, the mammary glands constitute an essential 

 part of the reproductive system, because it is through these that 

 the new-born is enabled to live for a time after its birth, before 

 it acquires the experience and power necessary to provide its own 

 food. The mammae ordinarily come into function at the time 

 when young are born. As soon as the young animals have 

 acquired sufficient age and strength to lead an independent ex- 

 istence, the glands cease to secrete milk, until their function is 

 aroused anew at the next period of birth. 



Following the general rule of vulnerability of organs, the 

 mammae are most subject to disease and accident during their 

 period of activity, and rarely suffer during their interval of rest. 

 The diseases of the milk glands may, accordingly, very properly 

 be dealt with as a part of obstetrics, because they not only jeop- 

 ardize the life and well-being of the mother chiefly during the 

 puerperal state, but also have great importance for the life of the 

 young at the beginning of its extra-uterine existence. 



Anatomically the milk glands of animals belong to the acinous 

 type. The glands consist of numerous acini or glandular vesi- 

 cles, lined with cuboidal epithelium. From each of these cells 

 there emanate small milk canals, which finally unite with each 

 other into common canals of larger size. These may empty into 

 a large cistern and thence through a common opening at the end 

 of the teat, Fig. 5A, p. 37, or two or more cisterns form, each of 

 which opens through a separate milk duct, or the milk canals 

 may remain separate, without milk cisterns and open directly at 

 the end of the nipple. There are consequently two great types of 

 milk glands— the one with a cistern, in which a considerable 

 volume of milk accumulates ; and the other without a cistern, 

 in which the milk canals lead from the glandular substance di- 

 rectly to the end of the teat. 



Solipeds, ruminants and swine have capacious milk cisterns ; 

 in carnivora milk cisterns are absent. The general anatomy of 

 the milk glands has been briefly outlined on page 35. 



The variations in the structure of the milk glands in different 

 animals are very interesting in relation to their tendency to disease. 

 The highly-developed glands of ruminants, with a single large 

 cistern and a very large excretory canal through the end of the 



939 



