BLOOD: ITS GENERAL PROPERTIES 89 



amount of protein present, this has been taken as a means of determining 

 variations in the concentration of the proteins. It has been found that 

 the concentration of the blood proteins varies somewhat; during ex- 

 ercise it is increased probably because of the taking up of water by 

 the tissues, and during profuse bleeding it is diminished because 

 large amounts of fluid are being added to the blood from the lymph, 

 which is relatively poor in proteins. The ingestion of considerable 

 amounts of salts has been found to reduce the concentration of the blood 

 proteins for a short time. In pathological conditions, as in diabetes, when 

 rapid changes in the body weight due to alterations in the diet are oc- 

 curring, changes in the fluid content of the blood are often observed. 

 Likewise in edema caused by faulty renal function, there may be a re- 

 tention of fluid in the blood before there is any indication of edema. The 

 hydremic condition of the blood can therefore be considered as a useful 

 diagnostic aid in determining the water metabolism. 



The relative concentration of the proteins of the blood is also of some 

 interest, especially since in certain diseases a considerable amount of 

 blood protein is lost. By refractrometric methods it is possible to sep- 

 arate the globulin and albumin fractions. Normally the total proteins 

 range between 6.7 and 8.7 per cent, of which the albumins lie between 

 4.95 and 7.7 per cent, and the globulins between 1 and 2.54 per cent. In 

 some diseases, as in chronic nephritis, pneumonia, and syphilis, the 

 total proteins of the blood are decreased and the relative amount of 

 serum globulin is increased On the other hand, in many mild infections 

 and chronic septic conditions the globulin fraction may be increased 

 with no change occurring in the total protein content. 3 



Our knowledge of the origin and the function of the blood proteins is 

 quite unsatisfactory. Previous to the discovery of amino acids, the 

 building stones of the proteins, in the blood it was thought that the 

 nitrogenous nutrients were converted somehow into blood proteins dur- 

 ing or immediately following their absorption from the alimentary 

 canal, and that the tissue cells were nourished from this common pro- 

 tein. It is now known that the amino acids are not immediately syn- 

 thetized into blood proteins after their absorption from the digestive 

 system. The blood proteins are radically different from the tissue pro- 

 teins. Substances which retard or accelerate nitrogen metabolism do 

 not alter the relationship existing between the protein bodies of the 

 blood. This fact indicates that the serum proteins have a function quite 

 independent of the nitrogenous metabolism of the body. They un- 

 doubtedly maintain the viscosity of the blood and assist in preserving 

 its neutrality. Attempts to localize the site of formation of the blood 

 proteins have not been successful. There is some evidence that fibrin- 



