LACTATION 573 



supposed to be derived directly by hydrolysis from certain 

 polysaccharide substances introduced in the food. It is pointed 

 out further, that such substances are present in plants which 

 form the normal diet of certain animals. It would appear, 

 however, that there is no direct evidence that lactose is actually 

 formed in this way. Moreover, this theory can scarcely be 

 applied to carnivorous animals, as Porcher 1 has pointed out. 



There is, therefore, but little evidence that lactose is ela- 

 borated in the mammary glands from any closely related carbo- 

 hydrate precursor carried thither from elsewhere in the body. 

 It is of course obvious that this sugar must be derived ultimately 

 from compounds contained in the food, and it would seem not 

 improbable that it is manufactured partly from protein sub- 

 stances, and not merely from other carbohydrates. 



THE NORMAL GROWTH OF THE MAMMARY GLANDS 



The growth of the mammary glands in the rabbit has been 

 described by Miss Lane-Claypon and Starling, from whose paper 

 the following account is taken. 2 



In the virgin animal of about eight to twelve months old 

 mammary tissue cannot ordinarily be detected with the naked 

 eye, but in stained preparations of the connective tissue sur- 

 rounding the nipple, it is possible to see the ducts which com- 

 prise the gland. These are generally restricted to an area of 

 not more than one centimetre broad. Sections show that the 

 gland at this stage consists entirely of ducts which are lined 

 with a single layer of flattened epithelium, and end blindly. 

 No traces of alveoli are to be seen in the gland. 



By the fifth day after conception a marked change has taken 

 place in the gland, which now appears, on reflecting the skin 

 from the abdomen, as a clearly differentiated pink area, circular 

 in shape, and surrounding the position of each nipple. The 

 diameter of this area is from about two to three centimetres. 



1 Porcher, " Sur la Physiologie de la Mamelle," Jour, de Med. Vet. de 

 I'ficole de Lyon, Sept. 30, 1905. 



2 Lane-Claypon and Starling, "An Experimental Inquiry into the Factors 

 which Determine the Growth and Activity of the Mammary Glands," Proc. 

 Roy. Soc., B. t vol. Ixxvii., 1906. See also Brouha, loc. cit. 



