MILK SECRETION 9 



the activity of the cells. In the formation of colostrum j the 

 albuminoid matter is greatly in excess of that after secretion 

 is well established, and with the decrease of albumin there is a 

 proportionate increase in casein. A ferment has been extracted 

 from the mammary gland which will convert albumin into 

 casein. 



The water, no doubt, passes directly from the capillaries into 

 the milk follicles, and carries with it the mineral constituents in 

 solution. 



The functions of the mammary gland are performed invol- 

 untarily. There seems to be some connection between the 

 mammary gland and the central nervous system, but how much 

 control can be exercised by will has not been determined. 

 Locally the stimulus seems to be the empty milk duct, for when 

 the ducts become full the secretion is partially checked, but is 

 considerably stimulated during the process of milking. 



RATE OF ACTIVITY IN MAMMARY GLAND (Bitting) 



Collier made an investigation 1 to determine the number of 

 fat globules found in milk in a given time. He made his obser- 

 vations on a large number of cows and found that on an aver- 

 age each secreted seven-tenths of a pound, or nearly 19.6 cubic 

 inches, of milk an hour, and that there were 152 fat globules 

 in each 0.0001 cubic inch of milk. He concluded that this was 

 equivalent to secreting 136,000,000 fat globules a second. He 

 duplicated his work on 23 other cows and found they secreted 

 an average of 138,200,000 fat globules a second. Collier also 

 recognized the fact that milk contains ingredients that must 

 be the result of some special activity, as the casein and milk- 

 sugar are not present in the blood and the fat only in traces, 

 thus precluding the possibility of being derived by transuda- 

 tion. A good cow may produce 2.5 kilograms (5 Ib.) of albu- 



1 New York State Experiment Station Report, 1891. 



