CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 783 



Average Composition of Milk in Different Animals. 



Woman. Cow. Mare. Bitch 



Casein &c. 2 4 2*5 10 



Fats 2-75 4 2 10 



Sugar 5 4'4 5 3'5 



Salts -25 '6 -5 5 



Total Solids 10 13 10 24 



Water 90 87 90 76 



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

 the height of lactation has been calculated at 700 to 800 cc. A 

 good milch cow will yield about 10 litres of milk per diem. 



514. 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 parturition. This milk differs from the 

 subsequent milk in microscopical characters 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 containing 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 corpuscles, 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-substance 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 favourable 

 temperature exhibit slow amoeboid 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 distinctly 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 colostrum corpuscles 

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



