614 COMPOSITION OF MILK. [Book n. 



from time to time, and besides undergoes marked changes dur- 

 ing the period of lactation. The relative general composition 

 of human milk and that of the cow, the mare, and the bitch 

 may perhaps be shewn by the following table : — but it is diffi- 

 cult to draw an average since the individual analyses given 

 differ so much; the figures given for casein and fat in the milk 

 of the bitch may be unusually high. 



Average Composition of Milk in Different Animals. 



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. 



§ 408. 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 imper- 

 fect 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 corpus- 

 cles.' Some of these closely resemble leucocytes, others are 

 either cells of about the same size, round or irregular, and pos- 

 sessing a nucleus, often misshapen, or are merely portions of 

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

 stance 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 



