382 EXTERNAL INTEGUMENT. 



In cow's milk, on the contrary, the fats and caseine are pre- 

 dominant: while mare's and ass's milk resemble human 

 milk more closely. 



The secretion of milk is essentially intermittent, and takes 

 place only under the influence of special conditions, connected 

 with the function of the genital organs : this function begins 

 in woman at the period of parturition, producing first the 

 colostrum, and, afterwards, the genuine milk. During its 

 long periods of repose, the gland becomes atrophied, as it 

 were ; this is its normal condition in young girls, in aged 

 women, and in men. It develops in women at the period of 

 puberty, but the mammary culs-de-sac and their globular 

 epithelium become distinct and well-defined only under the 

 influence of pregnancy and parturition ; the moulting, which 

 produces the milk, is only the last stage of this hypertrophy. 

 Direct excitation, under some peculiar circumstances, may, 

 however, give rise to this hypertrophy and moulting: young 

 unmarried women, on giving their breast to a nursing child, 

 have found this gland develop and produce milk, under the 

 exciting influence of suction, and a similar phenomenon has 

 been known to occur in the case of men. Finally, at birth, 

 both male and female children, by means of this same rudi- 

 mentary gland, secrete a fluid strongly resembling milk, and 

 which, no doubt, has some connection with the existence of 

 a similar fatty secretion (vernix caseosa) spread over the 

 whole surface of the body. 



These different phenomena, the first especially, prove that 

 the mammary secretion is a reflex phenomenon, but experi- 

 mental physiology has not yet pointed out through what 

 nervous organs this action takes place : experiments on the 

 intercostal nerves, and on the branches of the sympathetic 

 nerve, have yielded no results. 1 As might be supposed, the 

 food appears to have great influence on the production and the 

 character of the milk. Finally, it has been observed that 

 many medicines administered to the nurse reappear in the 

 milk, and this circumstance affords an excellent though 

 indirect method of acting upon the child. 



Messrs. Mayensen and Bergeret have, therefore, by a very 

 simple method of analysis, decided that a single, very small 

 dose, of mercury or mercurial salts will be eliminated in a 

 great measure in the lacteal secretion ; the mercurialization 



1 See Cl. Bernard, " Liquides de 1'Organisme." Vol. IT. p. 

 220. 



