Origin of Yield Mark. 49 



So the liight and width of the Yield Mark, also, are 

 generally according to the extent of milk weight pressure 

 in the udder below, and to the tension on the skin of the 

 twist above, the result being the formation of a Yield 

 Mark, in hight and width, according to the weight of 

 milk, and the size of the udder, as roughly shown in Plates 

 I. and II. 



The corrugations or furrows in the skin, met with in 

 large Yield Marks, that are formed by the weight strain 

 of large yield, are also the result of great and continued 

 strain on the skin of the twist, from the equally great press- 

 ure of milk weight in the bottom of the udder; the 

 weight of the milk glands, of course, combining with the 

 yield weight, according to natural gravitation. 



Gravity, or weight force, pertains to all matter, whether 

 in large masses or in small particles ; or, compounded in 

 a liquid form, as we find it in milk. The component in- 

 gredients of milk have as much weight after being min- 

 gled in the milk glands as before ; hence, there is always 

 downward pressure in the udder, in extent according to 

 the quantity of milk in the glands, with corresponding 

 strain on the inner skin layer and hair roots, in proportion 

 to the weight pressing down in the bottom of the udder, 

 so drawing down the root-ends of the hair, and forming 

 the Index or Yield Mark ; which makes the demonstra- 

 tion of the origin of the Yield Mark as a consequence of 

 yield itself, sufficiently complete. 



Enlargement of the Yield Mark. 



The Yield Mark is usually transmitted by hand-milked 

 cows, and is small in size, and would continue small on 

 heifers, as it does in the bull, if heifers inheriting the 

 mark were not hand-milked, but allowed to suckle their 

 calves in the natural way. As soon, however, as milking 

 at the pail begins, storing milk in the udder, for this pur- 



