BLOOD AND BLOOD DERIVATIVES — COHN 421 



cules increase the viscosity of solutions and may well bring about 

 abnormal distribution of plasma proteins. It is by no means certain, 

 therefore, that the retention of foreign substances of this kind in the 

 blood stream is beneficial. 



From a physicochemical point of view, it is possible to understand, 

 at least as a first approximation, certain of the phenomena of plasma 

 loss. Since all the plasma proteins have about the same equatorial 

 diameter, any change in the permeability of a membrane which would 

 permit one plasma protein to diffuse through it should permit any 

 of them to do so. Under these circumstances, the amount of plasma 

 protein of each type to diffuse should be an inverse function of their 

 length. Consequently for a given change in permeability there will 

 be a greater loss — and therefore a greater need for replacement — of 

 albumin than of the globulins or fibrinogen. 



Clearly there is a principle guiding the amount of any plasma com- 

 ponent that may wisely be used in replacement therapy, namely, the 

 amount that will tend to reestablish rather than to derange the normal 

 concentrations of the various physiologically significant plasma com- 

 ponents. 



CHEMICAL FRACTIONATION OF THE COMPONENTS OF PLASMA 



The highly siDecialized structure of the plasma proteins indicates 

 that each has a special function and that their colloidal properties, 

 which alone have thus far been considered, are but superficial manifes- 

 tations of their intrinsic nature. 



The proteins, as their name implies, are "of the first importance," 

 and this importance extends equally to the structure of cells and to 

 the processes of life. The role of these nitrogen-rich substances in 

 the nutritional cycle of plants and animals has long been appreciated. 

 Indeed, the elementary composition of "blood albumin" and "blood 

 fibrin" were being studied by the group of chemists that collected 

 around Liebig just over a century ago, and in 1841 Denis, a French 

 scientist, communicated to Liebig the separation of blood proteins into 

 albumins and globulins. 



Though less labile than cells, proteins also are labile. The molecules 

 that occur in nature were until recently not readily separated, purified, 

 concentrated, or dried, without change of structure or loss of function, 

 by the conventional methods of chemistry. 



