BLOOD AND H^MOPOIETIC ORGANS 91 



THE BLOOD PLASMA. 



The plasma, or fluid in which the corpuscles float, 

 consists essentially of certain proteins dissolved in a 

 solution of sodium salts. It contains in all about 10 per 

 cent, of solid matter, of which 8 per cent, is made up 

 of proteins. These proteins belong partly to the albumin 

 and partly to the globulin group. In the former are 

 serum albumin, in the latter serum globulin and 

 fibrinogen. Whilst one speaks of them in this collective 

 fashion, there can be no doubt that there are really 

 several albumins and several globulins present. The 

 proportion of serum albumin to serum globulin is in 

 man about 4J to 3, but the exact proportion varies 

 considerably in different animals. In the cold-blooded 

 animals, for instance, it is chiefly globulins which are 

 present. Of the part played by the albumins and 

 globulins respectively we know nothing, but one cannot 

 believe that it is a matter of indifference which pre- 

 dominates. ,Bunge has suggested that globulin is the 

 form in which protein circulates in the body for nutritive 

 purposes, whilst the albumin is the more constant basis 

 of the plasma ; but this has not yet been proven. Nor 

 do we know whence the proteins are derived. They can 

 hardly be built up directly from the protein of the 

 food, for they are apparently regenerated even during 

 starvation. It has been suggested that they are 

 ' secreted ' by the blood corpuscles, but it is quite as 

 likely that fixed cells in the body are able to help in 

 their production. Modern theories of immunity compel 

 us to believe that the blood may contain bodies, pre- 



