160 TYPES AND MARKET CLASSES OF LIVE STOCK 



up to the region of the hips, and thence to the vena cava and the 

 heart, the veins along the route being parallel to the arteries 

 through which the blood came, and being similarly named. The 

 other route is already familiar, leading out in front of the udder 

 through the large subcutaneous abdominal veins (milk-veins) 

 which pass through the chest wall and become a part of the in- 

 ternal thoracic vein, reaching the heart by way of the anterior 

 vena cava. The direction of the blood in the encircling veins at 

 the top of the udder is determined by the valves in the vessels. 

 The larger volume of blood passes through the milk-veins, thus 

 bringing them into great prominence. During pregnancy, the 

 pressure of the uterus tends to interfere with the circulation 

 through the posterior vessels, and this tends to further increase 

 the size of the milk- veins. Inasmuch as the blood may return to 

 the heart posteriorly, it is possible to have a large milker with 

 small milk- veins, but this is not likely to occur. Cows with 

 large milk-veins are large producers, and cows with small milk- 

 veins may be large producers. 



Nature and composition of milk. Cow's milk is an opaque, 

 yellowish-white fluid devoid of odor except for a short time 

 after its extraction. When fresh, it is slightly sweet and has a 

 slightly alkaline reaction. Under the microscope, milk is found 

 to be a fine emulsion of fat, a quart of milk being estimated to 

 contain 2,000,000,000,000 fat globules, and the cow that gives 

 two gallons of milk per day must therefore secrete at the rate of 

 over 175,000,000 fat globules per second. The composition of 

 milk varies a great deal; there are differences between breeds, 

 differences between individuals, and differences in the milk 

 from the same cow at different times. As lactation advances, 

 the daily milk yield decreases, but the percentage of fat con- 

 stantly increases as does the percentage of all solids. The 

 specific gravity of average milk is 1.032 and its composition is 

 as follows: 



f Water 87% 



f Ash .7% 



Milk I f Solids not Casein 2.7% 



Fat 9.1% I Albumin .7% 



[Solids 13 %\ I Sugar 5.0% 



( Fat 3.9% 



The results of various American experiments indicate that 

 the average composition of the milk of the various breeds is as 

 follows : 



