io THE GENERAL CHARACTERS OF THE PROTEINS 



from the peptones, both classes of bodies being intermediate 

 degradation products of natural proteins produced by means of 

 digestive enzymes. 



Owing to the unsatisfactory technique of using several salts, 

 Kauder, in 1886, for the first time carried out a fractional precipitation 

 of protein bodies, employing only one salt, viz. y ammonium sul- 

 phate. This research was undertaken under the direction of Hof- 

 meister, who, with his pupils, made valuable contributions during the 

 course of the next few years to the technique and knowledge of salt 

 precipitation. 



Kauder showed that the globulin precipitation in a serum solution 

 commenced when ammonium sulphate is present to the extent of 

 24-29 per cent, of complete saturation, and ended when the saturation 

 amounted to 36-46 per cent. 1 On filtering off the precipitate thus 

 produced and adding fresh quantities of ammonium sulphate, no 

 further precipitation took place until the degree of saturation 

 reached about 64 per cent. At this point the albumin fraction 

 commenced to be precipitated ; this precipitation was completed 

 when the degree of saturation reached 90 per cent. The point at 

 which precipitation of the various fractions commences and ends 

 varies somewhat ; it depends to a slight extent on the concentration 

 of the serum solution employed and its reaction. 



A series of systematic investigations was also carried out in 

 Hofmeister's laboratory with the object of determining the relative 

 value of various salt solutions as precipitants. The following 

 determinations are due to Lewith, who worked with the serum 

 proteins : 



IV. 



Albumin Precipitation. 

 Begins. Ends. 



33-6 47-2 



64-6 

 60-8 



More than 82*2 

 88-1 



The numbers in Columns III. and IV. express the amount of salt in grams per 100 

 c.c. of liquid. The strength of the protein indicates the percentage in the mixture after 

 addition of the salt solution. 



Some of the salts in the above table, such as ammonium 

 sulphate and potassium acetate, produce complete precipitation of 

 all the proteins in the serum solution ; others, such as sodium 

 chloride, potassium chloride and sodium nitrate, do not produce 

 complete precipitation of even the globulin fraction, when present to 

 the extent of complete saturation. 



Hofmeister investigated the relative influence of the acid and the 

 metal of the salt on the power of precipitating proteins. His results 

 are tabulated below. The numbers indicate the number of grams 



1 For experimental methods, see the end of this section. 



