38 MILK 



covered by cutting the gland. We do know that a milky fluid is 

 sometimes secreted from the glands of newborn infants, the so- 

 called witch's milk. This, together with the above-mentioned 

 cases of secretion from the gland of the male and occurrences of 

 virgin lactation, seem to lend support to the hypothesis of perma- 

 nent lactation ability of mammary glands. This idea is further 

 borne out by Pfaundler, who has reported virgin lactation in a calf 

 whose teats were sucked by its companions. A profuse secretion 

 resulted, which ceased to flow when the animals were isolated. 

 However, in all these cases the amount of secretion is small and 

 contains more water than normal milk. 



There is evidence of some particular influence stimulating the 

 mammary glands of the mother at the time of birth when the 

 gland enters on a period of full activity. It is the nature of this 

 influence that must be made clear. Two hypotheses suggest them- 

 selves and have found ardent supporters, namely, the stimulating 

 substances are either purely stimuh or their stimulating influence 

 is due to actual food value. 



Theories Depending on Purely Stimulating Substances.— 

 Advocates of this theory assume that hypothetic substances — 

 hormones — are discharged from the fetus or placenta into the cir- 

 culation. To the influence of these hormones they ascribe the 

 enlargement of the gland during the period of gestation. As sup- 

 port for this theory it is stated that marmnals instinctively know 

 that the placenta contains hormones and sometimes eat the pla- 

 centa after birth. Cattle raisers have beheved that milk secretion 

 is enhanced thereby and have encouraged cows in eating the 

 placenta. Hormones are said to exert their influence until the 

 gland is fully developed and enters upon active milk secretion. 

 However, this theory is not entirely in harmony with the fact that 

 in cases of premature birth milk appears before the gland is 

 fully developed. Gaines examined the udder of the goat mentioned 

 — the one that died before the birth of the kids. The udder was 

 undergoing rapid hypertrophy and was increased in size, but part 

 of this increase was due to accumulation of colostrum which exuded 

 freely from the cut ducts of the gland. This shows that there is 

 some secretion before birth, even though limited. Furthermore, 

 in late births, milk secretion is delayed. We are forced to the 

 conclusion, therefore, that there is an intimate connection between 

 birth and profuse milk secretion. Only when the fetus has died 

 has milk secretion been observed before actual expulsion. 



During the period of pregnancy, when the gland enlarges, secre- 

 tion is held in check, and consequently the assumption seems justi- 

 fied that, besides stimulating substances, inhibiting substances 

 are also present, or the same hormone stimulates growth of the 



