THE PHYSICAL PROPERTIES OF THE PROTEINS 9 



the pioneer in the systematic separation of the proteins by the 

 method of " salting out ". 



Denis included in his investigations not only proteins of animal 

 origin, but also bodies of a similar nature derived from plants. To 

 those proteins which are soluble in 10 per cent, sodium chloride 

 solution, from which they can be precipitated on dilution (especially 

 after saturation of the diluted solution with CO 2 ), Hoppe-Seyler 

 gave the name of " globulins ". They formed the subject of an 

 investigation carried out in Hoppe-Seyler's laboratory by his pupil 

 Weyl (1877), by whom the general reactions were clearly defined. 

 To this class belong vitellin, the protein derived from egg-yolk, the 

 protein first isolated from striated muscle by Kiihne, and called by 

 him myosin, the serum-globulin, and various plant proteins. Weyl 

 divided the globulins into two classes, viz., those which are soluble 

 in sodium chloride of high concentration (" vitellins ") and those 

 which can be precipitated from the 10 per cent, solution by saturation 

 with more salt (" myosins "). 1 



In addition to this work from Hoppe-Seyler's laboratory, 

 numerous other researches on the separations of proteins by salt 

 precipitation appeared between the years 1865 and 1885. 



Hammarsten investigated the precipitation of serum by sodium 

 chloride and magnesium sulphate, which only precipitate a fraction 

 of the proteins ; his investigations were supplemented by those of 

 Heynsius, 2 who some years later (1884) called attention to the great 

 precipitating power of ammonium sulphate ; in this respect it is far 

 superior to the corresponding sodium salt, which Starke (in Ham- 

 marsten's laboratory) and independently, Schafer, had a short time 

 previously shown possessed the power of precipitating proteins in the 

 filtrate from the magnesium sulphate precipitate. 



As a result of these various investigations, two classes of pre- 

 cipitating salts were introduced into general use for the separation of 

 proteins, viz., magnesium sulphate and sodium chloride, which 

 precipitate the so-called " globulin " fraction, and ammonium sul- 

 phate, which precipitates from the filtrate the " albumin " fraction. 



By the systematic application of these salts by Halliburton to the 

 separation of natural proteins of serum, muscle and milk, much 

 light was thrown on the constituents of animal tissues and fluids. 



Halliburton showed that serum could be separated into its 

 constituents by salts other than those already mentioned ; he found, 

 for example, that sodium nitrate, sodium acetate and sodium carbonate 

 could also precipitate serum-globulin, whilst potassium acetate and 

 potassium phosphate precipitated from serum all the heat-coagulable 

 proteins. He also applied the method of salt precipitation to 

 investigations on muscle-plasma and milk. He concluded that in 

 the former several proteins existed, whereas in the latter only two 

 could be recognised, viz., casein (or, as it is now termed, caseinogen) 

 and lact-albumin. 



Another application of the salt precipitation about this period 

 deserves to be mentioned. Wenz showed, in 1886, that peptones 

 were not precipitated by ammonium sulphate, and Kiihne and 

 Chittenden utilised this observation for separating the proteoses 



1 The present classification of the proteins is given in Dr. Plimmer's monograph. 



2 Ammonium sulphate had also been previously employed by Mhu. 



