FUNCTIONS OF THE MAMMARY GLANDS. 285 



dilating the central vascular trunks and depleting the periph- 

 eral capillaries. While the other part of the sweat-gland mech- 

 anism may, therefore, act normally, the impulse-waves lose 

 their influence. Finally, he remarks: "The analogy between 

 the sweat-glands of the foot and such a gland as the submaxil- 

 lary is, in fact, very close; . . ." so close, we may add, 

 that the existence of a common source of energy, a common 

 channel for its transmission, and a common peripheral mech- 

 anism can scarcely be doubted. 



MAMMARY GLANDS. Foster refers to the influence of the 

 nervous system upon the functions of the mammary glands in 

 the following words: "That both the secretion and ejection 

 of milk are under the control of the nervous system is shown by 

 common experience, but the exact nervous mechanism has not 

 yet been fully worked out. While the erection of the nipple 

 ceases when the spinal nerves which supply the breast are 

 divided, the secretion continues, and is not arrested even when 

 the sympathetic as well as the spinal nerves are cut." 



The nerves that supply these organs and the skin cover- 

 ing them are the intercostals from the second to the sixth, 

 inclusive; the thoracic branches of the brachial plexus; and 

 the descending branches of the cervical plexus, while sympa- 

 thetic filaments accompany all blood-vessels. 



In this analysis we will, in a measure, cover two subjects, 

 since the mammary secretion is carried on in a manner similar 

 to that which prevails in sebaceous glands. The functional 

 process in the latter and the similarity referred to are well 

 illustrated in the following quotations from the work of W. 

 Eoger Williams. 12 Eeferring to the sebaceous glands, this 

 author says: "Within the membrana propria of its secretory 

 part we find a stratum of small, irregularly-shaped epithelial 

 cells, each with a large nucleus (Fig. 1, &). The cells of this 

 region are constantly proliferating, and, as the products of the 

 process gradually shift toward the duct, they become changed 

 and gradually form the secretion." If the words that we have 

 italicized are placed in immediate sequence, they will be found 

 to exactly describe the histological arrangement of the sweat- 

 tubes from the delicate membrane to the lumen. "The steps 



12 W. Roger Williams: "Diseases of the Breast," London, 1894. 



