480 THE METABOLIC PROCESSES OF THE BODY. 



Average Composition of Milk in Different Animals. 



Woman. Cow. Mare. Bitch. 



The quantity of milk secreted by a woman in twenty hours at the height 

 of lactation has been calculated at 700 to 800 c.c. A good milch cow will 

 yield about 10 litres of milk per diem. 



428. Colostrum. This is the name given to the milk secreted at the 

 beginning of a period of lactation, just before and for some days after par- 

 turition. This milk differs from the subsequent milk in microscopical cha- 

 racters and in chemical composition. 



When ordinary milk is examined under the microscope hardly anything 

 is seen besides the fat globules except a very few imperfect cells or portions 

 of cells, consisting of cell substance more or less loaded with fat and con- 

 taining sometimes a more or less altered nucleus. A few minute granules, 

 thought by some to be particles of suspended casein or nuclein, are, however, 

 also visible. 



Colostrum, on the other hand, contains a large number of cells or cor- 

 puscles, which have been called " colostrum corpuscles." Some of these 

 closely resemble leucocytes, others are either cells of about the same size, 

 round or irregular, and possessing a nucleus, often misshapen, or are merely 

 portions of cell substance without a nucleus. In all of them the cell sub- 

 tance may be loaded with fat globules or may be fairly free from fat. Some 

 of these cells appear to be undergoing disintegration ; some may at a favor- 

 able temperature exhibit slow amo3boid movements, and must then at least 

 be regarded as living. 



Colostrum also differs from ordinary milk in containing not only a large 

 quantity of albumin (lactalbumin), but also a decided amount of globulin. 

 In consequence of this, colostrum differs from milk, inasmuch as it is dis- 

 tinctly coagulated by heat. 



As stated above, during the rapid growth by which the gland is enlarged 

 preparatory to lactation, the alveoli are at first solid masses of cells with 

 little or no lumen, and a lumen is established subsequently by the discharge 

 of the central cells. It is usually supposed that the cells so discharged, 

 some undergoing much, others comparatively little, change, supply the colos- 

 trum corpuscles just spoken of, and at the same time furnish the globulin 

 and excess of albumin also characteristic of colostrum. But this is not cer- 

 tain. The alveoli at this time contain peculiar cells resembling colostrum 

 corpuscles except that they are free from fat ; and it is suggested that these 

 being discharged and taking up fat in amoeboid fashion become colostrum 

 corpuscles. Some regard the colostrum corpuscles as simply leucocytes 

 which have similarly taken up fat. 



429. The mammary gland is present both in the female and the male 

 child at birth ; and in both sexes at and for a few days after birth is thrown, 

 in common with all the other secreting glands, into secretory activity, and a 

 small quantity of milk, the " witches' milk," so called by the Germans, is 

 discharged from the nipple. The milk resembles in all essential features 

 the milk of lactation. In both sexes this initial activity soon passes off, the 

 gland in the female further developing at puberty, but in the male remain- 

 ing, save in exceptional cases, in its infantile condition or somewhat retro- 

 grading. 



