LACTATION 577 



the difference between the glands in the two sexes is first mani- 

 fested at this time. The shght hypertrophy which occurs in 

 connection with each prooestrous period has been referred to, 

 while the great growth which the glands undergo during preg- 

 nancy has also been described. It would appear, therefore, 

 that the stimulus to mammary growth, which arises originally 

 in the ovary, is afterwards derived from the developing embryo. 

 This view is supported by the fact, which has been estabhshed 

 experimentally, that mammary development succeeded by 

 lactation after parturition can occur in animals whose ovaries 

 have been extirpated at about mid-pregnancy or even at a 

 shghtly earher period. 



It was formerly supposed that the connection between the 

 growth of the mammary glands and that of the embryo in the 

 uterus was a nervous one — that is to say, that the hypertrophy 

 of the glands was determined reflexly through the central nervous 

 system. There is now, however, abundant evidence that such 

 is not the case. This is shown, for example, by the experiment 

 performed by Goltz and Ewald,^ which has already been referred 

 to in considering the factors concerned in parturition. The 

 lumbo-sacral part of the spinal cord was completely exsected 

 in a pregnant bitch, so that all possible connection between 

 the mammary glands and pelvic organs through the nervous 

 system was destroyed. Pregnancy was accompanied as usual 

 by mammary development, and after parturition, lactation 

 occurred normally. Routh's case,^ in which normal lactation 

 took place in a woman with complete paraplegia below the 

 level of the sixth dorsal vertebra, has also been referred to 

 (p. 538). Moreover, it has been shown by Eckhard ^ that after 

 complete severance of the nerves (branches of the external sper- 

 matic) passing to the mammary gland, the activity of the latter, 

 and consequently the supply of milk, are in no way affected.* 



' See pages 490 and 538. 



' Ronth, " Parturition during Paraplegia, with Cases," Trans. Obstet. Soc. 

 vol. xxxix., 1897. 



' Eckhard, Beitrdge zur Anat. u. Phys., vol. i., Giessen, 1855. 



* Eokhard's experiments have been repeated by others with somewhat 

 contradictory results (see Basoh, loc. cit.); Kohrig ("Experimentelle Unter- 

 suohungen iiber die Physiologie der Milchabsonderung," Virchow's Archiv, 

 vol. Ixvii., 1876) found that the external spermatic nerve contained 



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