THE MECHANISM OF THE SECRETION OF MILK. 





 By E. A. SCHAFER. 



CONTENTS : General Considerations, p. 662 Influence of the Nervous System, p. 663 

 Action of Pilocarpine and Atropine, p. 664 Influence of Diet, p. 664 

 Place of Formation of the Organic Constituents, p. 665 Manner in which the 

 Secreted Materials pass out of the Cells, p. 665 Mechanism of the Discharge 

 of Milk, p. 667. 



THE composition of milk has been dealt with in a previous article 

 (pp. 125 to 140). Here it may therefore be simply noted, with regard 

 to its organic constituents, that these are remarkable in being peculiar 

 to the milk, not occurring in any of the other secretions or tissues of the 

 body (cf. however, footnote 1, p. 665), nor in foods which have not been 

 prepared from milk. The mammary gland-cells, therefore, unquestionably 

 form the products of secretion themselves from materials derived 

 through the lymph from the blood, and cannot be regarded, except as 

 concerns some of the inorganic substances, as acting merely as filtering 

 agents for allowing the passage of materials in solution from the blood. 

 And even with regard to the inorganic substances, 1 the proportion of 

 these is so different from that in which they occur in the blood and 

 lymph, that no filtration hypothesis appears in any way tenable even for 

 these. The gland-cells are further peculiar in that they only, as a rule, 

 function actively for a certain period after parturition, being at all 

 other times entirely inactive, although capable occasionally it is said 

 even in the male of being excited to activity by stimulation of the 

 nipple by a sucking action, such as that performed by an infant. Prior 

 to, and during such periods of activity, the whole gland becomes greatly 

 enlarged, both by an increase in size of existing alveoli, and also, perhaps, 

 by a sprouting, out of new alveoli. The cells lining the alveoli become 

 enlarged, and probably also multiply, for they are said to show evidence 

 of karyokinesis. 



The alveolar cells begin to accumulate within them granules, 

 partly of a proteid, partly of a fatty nature (although the latter may 

 more fitly be described as globules), and the alveoli get filled, before 

 there is any call for the pouring out of the secretion, with a clear fiuid 

 (coagulating to a finely granular material in pieces of the gland thrown 

 into alcohol), which contains a few fatty globules of different sizes, and here 

 and there cells filled with granules, staining with osmic acid, and appar- 

 ently identical with the colostrum corpuscles which are found in the milk of 



1 Bimge has shown that, with the exception of iron, the inorganic substances of milk 

 occur in nearly the same proportion as in the ash of new-born animals ("Text-Book," Woold- 

 ridge's translation, p. 107). 



