MANUAL OF OATTLE-FEEBING. 15 



being altered back into albuminoids, or of performing the 

 functions of the latter in nourishing the body. 



Albuminoids. — The albuminoids are found in manifold 

 modifications in all the organs and fluids of tlie healthy 

 body, except the urine, and all these modifications suffer 

 an almost continual mutual alteration under the influence 

 of the vital processes. 



Notwithstanding their diversity, however, they have 

 many and marked characteristics in common. 



As their name implies (albuminoid — albumin-like), they 

 resemble albumin or white of egg. Like it, they are des- 

 titute of any crybtalline form (amorphous). Most of them 

 exist in at least two modifications — a soluble and an in- 

 soluble one. In the soluble form they constitute, when dried 

 at a gentle heat, transparent, white or yellowibh solids, 

 destitute of taste or smell, and soluble in water ; in the 

 insoluble modification they form white, flocculent or fibrous 

 masses, insoluble in water, and, like the soluble forms, 

 having neither taste nor smell. 



The soluble albuminoids are very readily converted into 

 the insoluble form by a variety of means ; in some cases by 

 heat, in others by the action of acids or other bodies, and in 

 still others from some cause not yet known. This change is 

 called coagulation; it is apparently only a change in the 

 condition and not in the nature of the substance. At any 

 rate, it is not accompanied by any change in composition. 



Almost innumerable varieties of albuminoids have been 

 described, and much confusion exists as to theii\properties, 

 and relations to each other. For our present purpose, 

 however, it will suifice to indicate the three groups into 

 which these bodies may be classified — ^viz. : 



Albitmhi (represented by white of egg), Fibrin (repre- 

 sented by lean meat), and Casein (the basis of cheese). 



