516 PHYSIOLOGY CHAP. 



This result cannot be explained as a simple modification of 

 the blood circulation in the mammary gland, not only on account 

 of the time the pain lasts (which may be six hours), but also 

 because not only the quantity but also the quality of the milk is 

 altered : it becomes thicker and contains a larger amount of solids, 

 due particularly to increase of fat. 



Mironow further confirms Eckhard's observation that unilateral 

 section of the external spermatic nerve at the point at which it 

 leaves the pelvis has no appreciable influence on the total yield 

 of milk, nor upon the amount of milk secreted by the gland 

 operated on. 



But he adds two important observations, as follows: (a) 

 bilateral section of the external spermatic reduces the total yield 

 of milk by more than half (57 per cent) ; (5) the depressing action 

 of the pain after the bilateral division of these nerves continues, 

 showing that it is transmitted to the mammary gland by other 

 nerve paths. 



These nerve paths, according to Mironow, are represented by 

 nerve fibres that enter the mammae along with the branches of 

 the inferior epigastric vein and artery, and which he terms the 

 inferior epigastric nerves ; and further by a branch of a nerve 

 that accompanies a vein which ascends in the symphysis of the 

 pubes, and then divides into two branches to the two udders, 

 which he terms the azygos nerve. 



In excising these nerves as well as the external spermatics, so 

 as completely to isolate the mammary gland from the central 

 nervous system, Mironow did not succeed in suppressing the 

 lacteal secretion, but only in reducing it to about 35-45 per cent. 

 He also noted that after thus isolating the glands from the 

 central nervous system, the pain provoked by protracted sensory 

 excitation no longer affected either the quantity or the quality 

 of the milk. The inference is that the mammary gland must 

 have peripheral nervous centres which control the secretory 

 activity independent of the higher centres. 



A goat in which all the nerves to the udder had been cut 

 became pregnant and gave birth to two kids. The secretion of 

 milk increased during pregnancy, and after parturition gradually 

 regained almost the normal quotum obtained before the operation. 

 This led Mironow to think that the effect of pregnancy and 

 parturition on the development and secretion of the mammary 

 gland was not exerted reflexly by the brain and spinal cord, but 

 by the peripheral intermammary centres, possibly by modifica- 

 tions in chemical composition of the circulating fluids, due to a 

 special internal secretion of the uterus. 



Later physiological experiments confirmed the correlation 

 between the mammary gland and the genital organs. Halban and 

 Knauer (1900) saw that excision of the ovary was followed by 



