MAMMARY GLAND. 469 



some distance into the gland, when the breast is in a state of lactation. 

 These, which are much larger in many of the lower Mammalia than 

 they are in the Human female, seem to have for their office to contain 

 a store of milk, sufficient to supply the immediate wants of the child, 

 when it is first applied to the breast ; so that it shall not be disappointed, 

 but shall be induced to proceed with sucking, until the draught be oc- 

 casioned ( 836). 



831. The Mammary gland may be detected at an early period of foetal 

 existence, and it then presents no difference in the male and female ; 

 and it continues to grow, in each sex, in proportion to the body at 

 large, up to the period of puberty. At that epoch, however, the gland 

 begins to undergo a great enlargement in the female ; and by the age 

 of twenty, it attains its full size previous to lactation. Even then, how- 

 ever, the milk-follicles cannot be injected from the tubes. During preg- 

 nancy, the mammary glands receive a greatly-increased quantity of 

 blood. This determination often commences very early : and produces 

 a feeling of tenderness and distension, which is a valuable sign (where 

 it occurs in conjunction with others) of conception having taken place. 

 The vascularity of the gland continues to increase during pregnancy ; 

 and, at the time of parturition, its lobulated character can be distinctly 

 felt. The follicles cannot be readily injected, however, until the gland 

 is in a state of complete functional activity ; i. e., during lactation. < 

 The Mammary gland of the Male does not undergo this increase of deve- 

 lopment, except under certain peculiar circumstances to be presently 

 noticed ( 836) ; and it remains a sort of miniature picture of that of the 

 female, varying in diameter from that of a large pea to an inch or even 

 two inches. 



832. The Milk, secreted by the Mammary glands, consists of Water, 

 holding in solution the peculiar Albuminous substance termed Caseine, 

 and various Saline ingredients, together with (in most cases) a certain 

 form of Sugar ; and having Oleaginous globules suspended in it. These 

 globules appear to be surrounded by a thin pellicle, which keeps them 

 asunder, so long as the milk remains at rest. The existence of these 

 elements in ordinary Milk, as that of the Cow, is made apparent by the 

 processes to which it is subjected in domestic economy. If it be allowed 

 to stand for some time, exposed to the air, a large part of the oleagi- 

 nous globules come to the surface, in consequence of their inferior spe- 

 cific gravity ; and thus is formed the cream, whicji includes also a con- 

 siderable amount of caseine, with the sugar and salts of the milk. These 

 may be partly separated by the continued agitation of the cream, as in 

 the process of churning ; this, by rupturing the envelopes of the oil-glo- 

 bules, separates it into butter, formed by their aggregation, and butter- 

 milk, containing the caseine, sugar, &c. A considerable quantity of 

 caserne, however, is still entangled with the oleaginous matter ; and this 

 has a tendency to decompose, so as to render the butter rancid. It 

 may be separated by keeping the butter melted at a temperature of 180, 

 when the caseine will fall to the bottom, leaving the butter pure and 

 much less liable to change ; an operation which is commonly known as 

 the clarifying of butter. The Milk, after the cream has been removed, 

 still contains the greater part of its caseine and sugar. If it be kept 



