430 PHYSIOLOGICAL CHEMISTRY. 



The complex nature of the various organic matters has been referred 

 to in the preceding chapter, and will be more fully considered below; 

 but it may be mentioned here, that some of these organic substances 

 (or groups of substances) may be separated by a successive treatment 

 of the animal matter with various solvents. Thus, by treating with 

 ether or carbon disulphide, all fats may be extracted ; by then treat- 

 ing with alcohol and water successively other substances (generally 

 termed extractive matter or extractives) are dissolved, which may be 

 obtained by evaporating the solution. 



Among the extractives are found kreatin and kreatinin, urea, uric 

 acid, organic salts, etc. After the fatty matter and the extractives 

 have been removed there remains an elastic and somewhat horny 

 mass, which consists chiefly of proteids (albumin, fibrin, globulin, etc.). 



The complete separation of all substances is extremely difficult on 

 account of the great similarity in properties of many of these sub- 

 stances, and the rapid changes which they suffer when acted upon by 

 solvents or chemical agents. 



As the nature or composition of many of the inorganic salts present 

 in the animal tissues is changed during the burning off of the organic 

 matter, it is necessary to determine them either in the aqueous solu- 

 tion (extract) or by subjecting the animal matter to dialysis, by which 

 process they may be more or less completely separated from the organic 

 matter, which is left in the dialyzer, whilst the salts pass through the 

 membrane. 



Experiment 63. Cut a mouse (or some other small animal) into fragments 

 weigh and place them in a weighed dish ; expel all water by heating the dish 

 first over a water-bath, and then in an air-bath at a temperature of about 110 

 C. (230 F.) until there is no longer any loss in weight ; this loss is the amount 

 of water present in the animal. Disintegrate the dry pieces further by grind- 

 ing in a mortar and cutting with a pair of scissors, mix well and ignite a few 

 grammes in a platinum crucible until all organic matter is burned off and a 

 white or nearly white residue of inorganic matter is left. (Complete combus- 

 tion is facilitated by cooling and heating alternately several times, since the 

 animal charcoal, left after the first ignition, readily absorbs atmospheric oxy- 

 gen, which aids in combustion when again heated.) From the results obtained 

 by the ignition of the portion of dry animal matter calculate the organic and 

 inorganic matter of the animal operated on. 



Digest the inorganic residue with water, filter and test in the filtrate for 

 chlorides by silver nitrate. Dissolve the residue upon the filter in dilute hydro- 

 chloric acid and test portions of this solution for phosphoric acid by means of 

 ammonium molybdate ; for iron by potassium ferrocyanide ; for sulphuric acid 

 by barium chloride, and for calcium by adding an excess of sodium acetate 

 and then ammonium oxalate. 



