630 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



second, a much larger branch, termed the papillary branch, which is 

 distributed to the nipple; third, one, or occasionally two, glandular 

 branches, which are supplied to the walls of the milk-ducts and the 

 cistern. 



According to Rohrig, section of the papillary branch produces no 

 change in the milk secretion, but simply causes relaxation of the nipple. 

 Irritation of the peripheral end of this nerve causes erection of the 

 nipple without change of glandular secretion, while irritation of the cen- 

 tral end of this nerve produces considerable increase in the secretion. 



Section of the glandular branch, on the other hand, produces slow- 

 ing of the amount of secretion by causing relaxation of the walls of the 

 duct, while stimulation of this nerve may increase twenty -fold the secre- 

 tion of milk by causing contraction of the milk-ducts and consequent 

 discharge of their contents. 



Section of the inferior branch produces great increase in the amount 

 of milk secreted, while the stimulation of the peripheral end of this 

 nerve produces arrest of secretion. 



The explanation of these two classes of phenomena are understood 

 through a study of the character of this nerve. The median branch is 

 a compound nerve composed of both sensory and motor fibres, the latter 

 being especially found in the papilla^- branch distributed to the nipple, 

 while the glandular branch is almost solely motor. When the papillary 

 branch is stimulated it produces, by a reflex action, the contraction of 

 the muscular fibres of the excretory ducts, and so causes discharge of 

 their contents, while it also, in all probability, acts through the inferior 

 branch, and by it also increases the amount of milk formed in a manner 

 to be referred to directly. 



When the glandular branch is stimulated the muscular fibres of the 

 ducts contract, and, although no more milk may be actually formed, 

 there is, nevertheless, an increase in the amount poured out through 

 the contraction of the walls of the milk-ducts. 



On the other hand, the inferior branch is a vaso-motor nerve. When 

 its peripheral termination is stimulated, the milk secretion is arrested 

 through the constriction of the blood-vessels supplied to this gland. 



On the other band, when it is divided, the blood-vessels become 

 greatly relaxed, more blood passes through the organ, and its activity is 

 largely increased. 



Whether any of these processes are associated with the action of 

 true secretory nerves is not known, but from analogy, from what we have 

 seen in the case of the salivary gland, it ma}' be assumed that such is the 

 case. 



The explanation of the connection long known between the mechan- 

 ical irritation of the nipple, as in suckling and milking, and the increased 



