60 THE FEEDING OF ANIMALS 



this coagulation is mechanically unlike, at least, with 

 milk from different species. The action of this ferment 

 on casein is utilized in cheese-making in the development 

 of a curd which, with its inclosed fat, is separated 

 from the whey and pressed into compact masses and 

 later allowed to undergo certain changes due to other 

 ferments. 



Other phospho-proteins exist, one being the vitellin 

 in the yolk of eggs which, as prepared, contains 

 lecithin. 



77. Haemoglobin. Blood contains a peculiar com- 

 pound known as haemoglobin. When decomposed, it 

 separates into a protein, globin, and a coloring matter 

 haemochromogen, which, when charged with oxygen, is 

 called hsematin. This oxidation changes the haemoglobin 

 to oxy-haemoglobin. This haemoglobin in the blood of 

 mammals contains, besides carbon, nitrogen, oxygen, and 

 hydrogen, sulfur and iron. The latter varies in per cent 

 from .34 to .48, and sustains an essential relation to the 

 functions of the blood. The blood pigment has the 

 property of taking up and releasing oxygen with great 

 readiness, carrying its load of oxygen out of the lungs, 

 giving it up to oxidation processes in various parts of the 

 body, and bringing to the lungs in its place the result- 

 ing carbon dioxid to be discharged into the air. The 

 blood changes color with the acquisition and loss of the 

 oxygen. 



78. Lecitho-proteins. From the yolk of eggs, the 

 mucous membranes, and the kidneys, and doubtless from 

 other sources, are obtained a conjugated protein con- 

 taining lecithin. The constitution and special function 

 of this body are not well understood. 



