590 THE PHYSIOLOGY OF REPRODUCTION 



calculated that the udder of a cow could not contain the quantity 

 of milk which can be obtained from it at one milking, so that in 

 such cases at least it seems certain that the process of secretion must 

 be carried on during the time that the milk is being drawn. 

 Furthermore, the milk which is drawn latest has be.en shown to have 

 a different composition from that which is first obtained, the proportion 

 of solids to liquids undergoing an increase as the process of milking 

 is continued. This, however, is believed to be due partly to the 



FIG. 163. Section of mammai'y gland (human) during lactation 

 (highly magnified), a, Acini ; b, duct. 



larger globules of fat meeting with greater resistance in passing 

 through the ducts and so being retained until the end of milking. 

 Lehmann 1 has recorded an experiment in which a solution of sulphin- 

 digotate of sodium was injected into a vein of a goat which was 

 immediately afterwards milked. By the time the udder had been 

 almost completely emptied, a blue tinge appeared in the milk. After 

 an interval of about an hour and a half the animal was again milked, 

 when it was found that the injected sulphindigotate had penetrated 

 in sufficient quantity to render the milk quite blue. 



1 Lehmann, "Beitrage zur Physiologic der Milchbildung," 

 l,'ifti;,-li>'H Versucfa-Stationen, vol. xxxiii., 1887. 



l)ii- landtrirtk- 



