48 DAIRYING 



determined by the gland lobule cells, just as the color and variety 

 of an apple is a characteristic of certain cells in each bud. A 

 change of food of the tree will have no effect on the color or the 

 other normal characteristics of. the fruit of that tree. A Baldwin 

 tree contains cells that produce a Baldwin apple ; and green colored 

 appLes as well as red apples are produced on trees side by side in 

 the same orchard. The nature of the cells determines the char- 

 acteristics of the fruit, and no amount of food in the way of a 

 fertilizer can change this quality.- In the same way each cow is 

 born with cells in her milk glands that secrete milk ot a certain 

 composition, and no amount of feed or lack of feed will change 

 their character so long as the cow is in normal condition; more 

 feed will produce more milk by making these glands more active 

 or by building up a larger number of cells, but the milk secreted 

 will always have the same characteristic composition. If this were 

 not true it would be possible to make a cow give cream by feeding 

 a suffciently concentrated feed, and we could by changing the feed 

 obtain either Jersey or Holstein milk from the same cow. It may 

 be asked how does it happen that we have Jersey and Holstein milk 

 if feed does not change its richness, and why is not the milk of all 

 cows of the same percentage of composition? The answer to this 

 question is that there is a variation in the cell structure character- 

 ictics of the milk glands of cows when born and by selecting 

 animals that give a little richer or a thinner milk than the mother, 

 a strain of cows has been developed that after a few generations 

 give milk of a different percentage composition than that of the 

 first cow. The change in the per cent of fat (which is the most 

 easily varied of any of the milk constituents) is accomplished in 

 much the same way as the change in the color of a cow's hair. 

 There is no change during the life of one -cow in this particular, 

 but her offspring may be of a slightly different color than its moth- 

 er, and succeeding generations will show still greater variations 

 from the original animal if careful selections are made with this 

 point in mind. 



206. The Milk Glands are located in the udder near the body 

 of the animal as shown in Plate 8. Blood circulates through the 

 arteries and veins to the gland lobules which takes substances in the 

 blood and convert them into milk by means of microscopical 

 bodies called alveoli. When milk is being produced by the gland 



