226 ORGANIC AGRICULTURAL CHEMISTRY 



EXPERIMENT STUDY XXX 



Blood 



(i) Oxalated Blood. Secure some blood from a horse or cow and 

 let it flow directly into a lo per cent solution of ammonium oxalate. 

 The blood will remain unclotted and may be examined under high 

 power microscope for blood corpuscles. (See Hawk, " Practical Phys- 

 iological Chemistry" (1913), p. 197, for plates showing corpuscles.) 



(2) Fibrin. Draw off another quantity of blood, 100-200 c.c, and 

 immediately whip or stir it vigorously with some fine glass rods or a 

 small bundle of twigs or a bunch of stout cord tied on to a stick and 

 with loose ends like a mop. When clotting has been effected and the 

 fibrin has adhered to the rods or string, remove the beater and wash 

 the fibrin as clean as possible from all other material. Examine the 

 fibrin as to general character and make the protein tests with it as in 

 Experiment XVIII, 4. 



(3) Defibrinated Blood. The blood from which the fibrin has been 

 removed may now be examined for blood corpuscles and for other 

 constituents such as sugar, chlorides, etc. 



URINE 



Urine differs from milk in being considered as an excretion, 

 not as a secretion. It is the medium by means of which the 

 nitrogenous products of protein metabolism are removed from the 

 body. When the food nutrients are oxidized in the cells, the 

 carbon dioxide and water, resulting from the carbon and hydro- 

 gen of the fats and carbohydrates and also from a portion of 

 the carbon and hydrogen of proteins, is excreted in the exhaled 

 breath. All of the nitrogen and some of the carbon and hydro- 

 gen of the protein oxidation yield products which find their 

 way into the urine and are excreted in this way. The nitrogen 

 content of urine becomes, therefore, a measure of the protein 

 metabolism in the animal body. The nitrogen compounds in 

 urine are more or less complex compounds, containing carbon 

 and hydrogen together with the nitrogen, and they consequently 

 possess the possibility of being oxidized. This means that all 

 of the energy of oxidizing proteins is not yielded in the cell 



