490 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



Its other characteristics have been described under the head of 

 Gastric Digestion. 



To detect the presence of peptone in blood-serum, all the other albuminoids 

 must first be removed. • This may readily be accomplished by adding a solution 

 of acetate of iron, to which a few drops of sulphate of iron solution have been 

 added. The serum must first be diluted with five to eight volumes of water, heated 

 on the water-bath, and the iron solution and then caustic soda added, until only 

 a faint acid reaction remains. A thick, brown precipitate then falls, and the 

 supernatant fluid is free from iron and all albuminoids but peptone, the presence 

 of which may be recognized, after filtration, by the biuret reaction. 



Peptone is only found in the serum during and shortly after albu- 

 men absorption. 



Other Organic Constituents of the Serum. — Sugar may be detected, 

 after removal of albuminoids, by the copper test. Sugar is a constant 

 constituent of the serum of blood. Its origin and importance will be 

 discussed later. Ox-blood contains 0.543 pro mille sugar, sheep's blood 

 0.521 pro mille, dogs' blood 0.787 pro mille. 



Fat has already been mentioned. It is found only in scanty amount, 

 except after a meal, being in largest amounts in the serum from suckling 

 animals. Stearin, palmitin, and olein, with their respective soaps, are 

 the principal representatives. The odor of serum is probably due to a 

 volatile body of the fatty acid series. The yellow color of serum is due 

 to the presence of a special pigment. 



Lecithin is a constant constituent of the ethereal extract of blood- 

 serum. A large proportion of the phosphoric acid of the serum is con- 

 tained in this booty. Its origin and uses are not well understood. 

 Perhaps, since it is the carrier of phosphorus, it is of special importance 

 in the nutritive processes of bone. 



Cholesterin is also found in the ethereal extract of blood-serum, from 

 which it coagulates in white, pearly flakes. 



Further, small amounts of urea are found in serum, as well as 

 kreatin, kreatinin, and other products of the retrograde metamorphosis 

 of tissues, which will subsequently claim attention. 



The Inorganic Constituents of Blood-Serum. — Serum yields about 

 0.75 per cent, of ash, in which the following bases are found : Na, K, 

 Ca, Mg, Si, and Fe and P 2 6 H 2 , H 2 S0 4 , C0 3 , and CI. K and Fe are in 

 extremely minute quanta ; Mg and Cain somewhat larger quantity, 

 though out of proportion to the richness of the organism in these bodies. 



The Gases of the Blood. — Oxygen, carbon dioxide, and nitrogen are 

 found in the blood in conditions of loose chemical union with certain 

 blood constituents (haemoglobin) and in solution in the blood-plasma, 

 which, like other fluids, is capable of dissolving a certain amount of 

 different gases. Their consideration will be reserved for the chapter on 

 Respiration. 



