94 Anatomy and Physiolocjy of the Mammary Gland. 



of the duct, both contractile and areolar tissue are developed ; 

 the latter forming a bond of union, in which numerous bloodvessels 

 ramify. 



Such are the chief points of interest in the anatomy of the 

 mammary gland and its appendage, tlie teat, and having described 

 these we proceed to speak of the secretion of milk. 



The Milk. 



The colour and general condition of this fluid are so well 

 known that it is unnecessary to enter into any particulars 

 respecting them. Of all the secretions which are elaborated 

 from the blood, tliere are none which come so near to it in 

 chemical composition as milk. This circumstance, however, 

 ceases to be a matter of any surprise when we come to reflect 

 on the fact that milk is the sole nutriment of the young animal, 

 both immediately after, and for several weeks succeeding, its 

 birth. Indeed, milk may be said to be but blood in another 

 form. Dx". Abernethy used to remark that it was ''''the most 

 'nutritious of all t/iinys,'' and in the language of Prout we may 

 say, that it is '• the true type of all food." On this point Dr. 

 Carpenter, in his ' Manual of Physiology,' has wisely expressed 

 himself by obser\ ing that milk being " an admixture of albu- 

 minous, saccharine, and oleaginous substances, indicates the 

 intention of the Creator that all these should be employed as 

 components of the ordinary diet.'' Besides this mixture of 

 nitrogenous and non-nitrogenous matters, so essential to the 

 maintenance of life, the saline or inorganic matters also Avhich 

 milk contains are no less necessary to the growth or development 

 of the young animal. These also are nearly identical with those 

 of blood, with a greater proportion, however, of the phosphates 

 of lime and magnesia — salts, especially the former, which enter 

 largely into the composition of bones. 



The albuminous portion of milk is met with in the form of 

 caseine, which is held in a state of solution in the water of the 

 fluid, as are also the salts and saccharine matters. The oleaginous 

 substances, on ttie contrary, exist in the form of globules, which are 

 rendered visible by the microscope, and when the fluid is thus 

 examined they are found to be floating freely in it, without any 

 tendency to coalesce or run together. Fig. 7, which we here insert, 

 gives the ordinary appearance of healthy 2Tiilk, when examined 

 by a highly-magnifying power. It will be seen that the globules 

 vary considerably in size, some existing in the form of mere points, 

 while many of the larger attain a size of oqW^'^ ^^ ^^ inch, their 

 average dimensions being ^-^'^^^tli of an inch. In proportion 

 as milk is rich in butter, so are the globules present in increased 

 number and size. The colour and opacity of milk are both due 



