356 PHYSIOLOGICAL CHEMISTRY. 



phide, all fats may be extracted ; by treating then with alcohol 

 and water successively other substances (generally termed extrac- 

 tive matter or extractives) are dissolved, which maybe obtained by 

 evaporating the solution. 



Among the extractives are found kreatin and kreatinin, urea, 

 uric acids, 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 (albu- 

 min, fibrin, globulin, etc.). 



The complete separation of all substances is extremely difficult 

 on account of the great similarity in properties of many of these 

 substances, 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 solution (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. 



Blood. Two kinds of blood are distinguished, the arterial or 

 oxidized and the venous or deoxidized blood. Arterial blood 

 as it is present in the system, or immediately after it has been 

 drawn from the body, is a red liquid of an alkaline reaction and 

 a specific gravity of about 1.060. Upon examination under the 

 microscope, blood is seen to consist of a colorless fluid, called 

 plasma or serum, in which float small globules 'or corpuscles. 

 These corpuscles are capable of transmitting red light only, thus 

 imparting to the blood its red color; their shape is that of a 

 biconcave disk, and their size about -g-g^, of an inch in diameter. 

 Besides the red corpuscles, there are found some of a white 

 color, but their number is very much smaller, the proportion of 

 white to red corpuscles being about 1 to 350. 



The composition of normal human blood is about: 



Water, 79.50 per cent. 



Serum-albumin, 7.34 



Fibrin, 0.21 



Haemoglobin, 11.64 



Fatty matters, 0.18 



Extractives, 0.32 



Ash, 0.81 



