158 COLLOIDS IN BIOLOGY AND MEDICINE 



Globulin. 



Those proteins which are insoluble in pure water and soluble in 

 salt solutions are called globulins. They are constituents of the 

 blood serum r eggs and milk of animals. They occur in other organs 

 in traces, thus, e.g., thyreo-globulin, the iodin-containing protein of 

 the thyroid, is a globulin. Large quantities of globulin are found 

 stored in the seeds of plants. A seed globulin, edestin, has been 

 obtained in crystalline form. 



If serum is dialyzed against pure water, globulin will be precipitated 

 as the content of the dialyzer cell (globulin) parts with salt. By 

 ultrafiltration, H. BECHHOLD* 4 was able to separate globulin from the 

 common salt holding it in solution. Globulins are also soluble in acids 

 and alkalis. If globulins are kept undissolved (e.g., dried or sus- 

 pended in distilled water) a change occurs ; they lose more and more of 

 their solubility in dilute solutions of neutral salts. Like the albumins, 

 globulins are amphoteric: without the presence of salt they have no 

 definite direction of migration; in the presence of traces of alkali 

 they pass to the anode and in the presence of acids they pass to the 

 cathode. According to L. MICHAELIS, an H ion concentration of 

 4.10~ 6 is the isoelectric point for serum albumin: According to W. B. 

 HARDY,* 1 a given quantity of salt-free globulin is dissolved by an 

 equimolecular quantity of strong monobasic acids (HC1, HN0 3 , 

 monochloracetic acid) . The weaker the acid the more of it is neces- 

 sary to dissolve the globulin. About twice as much sulphuric acid, 

 tartaric acid and oxalic acid, and three times as much phosphoric 

 acid and citric acid, is required than of HC1. W. B. HARDY concludes 

 from this that globulins form salts with acids which in the case of 

 weak acids are greatly hydrolyzed. 



Bases act in a manner similar to the acids, with the exception 

 that NH 3 dissolves as much globulin as NaOH. 



Rise of temperature increases the hydrolysis, i.e., globulin, dis- 

 solved in an amount of weak acid or weak alkali just sufficient to 

 give a clear solution, becomes turbid when it is warmed; however, 

 the process is not completely reversible. 



It was deduced from the conductivity values of alkali globulin that 

 globulin is a pentavalent acid, and from its saponification with 

 methyl acetate as well as its action in the inversion of cane sugar, 

 that it is of a more strongly acid than basic character. This is also 

 evident from the fact that the conductivity of its acid salts increases 

 progressively more, when diluted, than the conductivity of its alkali 

 salts. The preponderant acid character is also evident from the fact 

 that litmus is reddened by globulin. 



