144 MAMMARY GLANDS. 



by polluted water used either to dilute the milk or to wash the 

 cans which contained it ; scarlet fever, also, has been contracted 

 by those who have drunk milk which had become infected by the 

 hands of milkers who were recovering from the disease. Diph- 

 theria has also been transmitted through infected milk. 



In order to prevent the fermentation of milk, the bacteria con- 

 tained in it should be destroyed. This may be done either by 

 sterilization or pasteurization. 



Sterilization consists in heating the milk to 100 C., the boiling- 

 point, by which the milk becomes " sterile" that is, all organisms 

 which would produce fermentative changes in the milk are killed. 

 The objections to this process are that the taste of the milk is 

 altered to that of boiled milk, the casein is not so easily digested, 

 the ernulsification of the fat and its absorption are not so readily 

 brought about, and the amylolytic enzyme is destroyed. If the 

 exposure to the heat continues too long, the milk becomes brown- 

 ish in color, due to the conversion of lactose into caramel. 



In pasteurization the milk is exposed to a temperature of 

 only 71 C. to 76 C. for fifteen to twenty minutes; milk thus 

 treated is not changed as in sterilization, but will keep only a short 

 time a day or two. 



Human milk is the product of the mammary glands, the 

 structure of which may here be concisely described. 



MAMMARY GLANDS. 



The mammary glands or mammae (Fig. 87) are two in number, 

 situated one in each pectoral region. They are compound racemose 

 glands, and consist of gland-tissue which is made up of lobes, and 

 these again of lobules (Fig. 88). The lobes are connected by 

 fibrous- tissue, and between them is fat. Each lobule is composed 

 of sacculated alveoli and a duct, the lobular duct. The lobular 

 ducts discharge into larger ducts, which in turn discharge into a 

 lactiferous duct, which may be regarded as the excretory duct of 

 a lobe. Of these ducts, tubuli lactiferi, there are from fifteen to 

 twenty. They open at the surface of the prominent point of the 

 breast, the mammilla or nipple, surrounding which is the areola, 

 which in the virgin is of a pinkish color, becoming darker during 

 pregnancy and almost black at its termination. Under the areola 

 the tubuli lactiferi are dilated, forming ampullae, in which, during 

 the period of lactation, the milk accumulates in the intervals of 

 nursing. When these reservoirs are full the tension of the gland 

 stops the process until they are emptied by the sucking child, 

 when the cells again take on their function and the milk is 

 secreted and flows into the ampullae through the ducts, there to 

 accumulate until the next nursing. 



