88 THE BLOOD AND THE LYMPH 



a suitable amount of water, which makes the salt adherent to the pre- 

 cipitate a weak saline solution. In neutral or acid solutions it is coag- 

 ulated by heat at about 75° C. But it does not act as an individual pro- 

 tein, since a portion of it is precipitated by dialysis or by carbon diox- 

 ide. Probably serum globulin really consists of two or more proteins. 



The serum albumin remaining in solution after saturation with am- 

 monium sulphate likewise does not represent a chemical entity. It is 

 possible by carefully heating the solution of serum albumin to distin- 

 guish three separate coagulation temperatures. This fact has been in- 

 terpreted as meaning that the serum albumin consists of at least three 

 closely related proteins. 



Since the refractive index of the blood depends primarily upon the 

 amount of protein present, it 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 \ r aries 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 some 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 

 4.05 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- 



