296 CHEMISTRY OF THE PROTEIDS CHAP. 



view cannot be upheld, because by the addition of neutral salts the 

 C0 2 normally present in water is discharged, and therefore the alkali 

 which is added will not be partly bound by the acid, and in con- 

 sequence will produce a stronger effect on the litmus. The author 

 arrived at this conclusion by adding neutral litmus solution to the 

 distilled water, and then boiling it to get rid of the C0 2 , and his conclu- 

 sions are supported by the criticism of Starke's paper in Wolff and 

 Smits' article. 1 



6. Precipitation due to a Removal of Salts 



Proteids, which require the presence of neutral salts to remain 

 in solution, are widely distributed amongst both plants and animals, 

 and are represented by the globulins proper arid the closely allied 

 muscle-proteids (paramyosinogen and myosinogen). These substances 

 are precipitated from their solutions either if the salts normally 

 present are removed by dialysis, or if the concentration of the inorganic 

 salts is greatly diminished by the addition of water. Various causes 

 have been assigned for this precipitation. 



W. Pauli 2 has studied the effect of both non-electrolytes and of 

 electrolytes on globulin solutions. He found pure water containing 

 grape-sugar in quantities varying from mere traces up to 3 '2 5 normal 

 = 6 8 '5 per cent, or containing pure urea up to three or four times 

 normal strength, always precipitated globulin as if neither sugar nor 

 urea had been present, and the globulin which separated out in these 

 solutions could always be readily dissolved by the addition of neutral 

 salts. He drew the conclusion that globulin requires for its solution 

 the presence of a neutral salt which has dissociated into its ions, and 

 that the non-dissociated molecules of a salt play no part. The ion- 

 action depends on the number of ions present and on the quantity of 

 the globulin, for only that amount of globulin passes into solution for 

 which sufficient salt has been added, and the subsequent clearing of the 

 globulin solution is proportional to the amount of salt added. 



The fact that free ions render globulin soluble leads Pauli to sup- 

 pose that the negative and positive ions unite with the proteid-molecules 

 in a loose, chemical manner, the kat-ions attaching themselves to certain 

 radicals in the proteid, while the an-ions join on to other groups. This 

 supposition is supported by the following analogous case, which was 

 pointed out to Pauli by Hofmeister: Amino-acids unite simultaneously 

 with both alcohol and hydrochloric acid to form beautifully crystalline, 



1 K. Wolff u. A. Smits, Zeitschr.f. Biol. 41. 437 (1901). 



2 W. Pauli, Pfiuger's Arch. 78. 315 (1899) ; compare also with W. Huiskamp, 

 Zeitsch. f. physiol. Chem. 34. 32 (1901). 



