62 The Feeding of Animals 



and cools it clots, a phenomenon which is nothing more 

 than the formation of strings of fibrin. Fibrin as such 

 is not found in living blood, but is one of the prod- 

 ucts into which fibrinogen splits when exposed blood 

 cools, probably because of the influence of a ferment. 

 Stranger than all is the fact that so long as the blood 

 is retained in the arteries and veins, even if the animal 

 dies and grows cold, this clotting does not appear. 



Serum globulin is a collective name for several glob- 

 ulins, which exist in blood serum and in the other fluids 

 of the animal body, such as lymph and its allies, in- 

 cluding those exudations which pertain to diseased 

 conditions, especially dropsical. 



One more proteid has been generally classified as a 

 globulin, although differing in some respects from the 

 other members of this class. Reference is made to 

 vitellin, which is the principal proteid in the yolk of 

 eggs. It is there intimately mixed with certain pecu- 

 liar phosphorized bodies, which we shall notice later. 



The modified albuminoids. All of the proteids pre- 

 viously noticed may properly be called simple, native 

 proteids. This characterization is appropriate because 

 these are the bodies that possess the typical reactions 

 and qualities of the albuminoids as a class, and are the 

 principal ones found in the normal tissues of plants 

 and animals. They are the basal substances from 

 which others appear to be derived after modifications 

 of one kind or another. It seems proper, therefore, to 

 speak of certain other proteids as modified albuminoids, 

 because, through various influences, either natural or 

 artificial, they have acquired chemical and physical 



