22 Cattle Problems. 



ward i)rcssur(.- in the udder sack, being coequally constant 

 witli the tension of the milk-weight; the size, and weight 

 pressure of the milk glands increasing with the cjuantity 

 and weight-strain of yield, at all times. Thus, while the 

 udders of milk cows that are making an increasing yield 

 are being extended forward by expansive or centrifugal 

 force, gravitation, or weight of milk, combined with gland 

 weight, is as constantly increasing the depth or downward 

 extension of the bag. 



See Plate III. , Figs. 3 and 5 . 



The relaxation of the udder sack becomes so conspicu- 

 ous in large milkers, in some instances, as to make it evi- 

 dent that the combined influence of expansion and weight 

 tension together have overborne the natural contractive 

 force of the udder skin, thus permanently enlarging the bag 

 by destroying, or, at least effectually suspending, its natural 

 and necessary contractibility. This result is clearly shown 

 in the uncontracting bags of cows that are dried only with 

 great difficulty, and breed but seldom or fail to breed at 

 all. The skin or sack of the udder is, of course, thinned 

 down, as yield and size of bag increase, and this, when 

 carried to excess or effected too rapidly, is doubtless the 

 chief cause of loss of contractile power in the udder skin. 



Increase of feed being the cause of increased yield, such 

 feed as adds to the bulk of blood increases yield and the 

 size of the udder together. Thus succulent feed, like grass 

 and roots, tends to enlarge the yield and the bag, and in 

 this will be found a reason for the largest milk-producing 

 cows being generally found in the best natural grass local- 

 ities, in both dry and humid climates. Thus the best grass 

 countries in America do, or surely will with equal care and 

 training, produce the largest or best yielding cows as a rule. 

 The best natural grass districts of this country are in fact 

 naturally our best dairy localities, and in these, according- 



