CONCENTRATION OF SERUM. 187 



tion of 1 c.c. of serum, over 0.5 per cent, may be 

 suspected. 



Other toxins and bacteria are discovered by 

 intraperitoneal injection of guinea-pig. 



For therapeutic purposes, it is desirable to have 

 a serum of high value in order to avoid giving too 

 large quantities. Several diphtheria serums are 

 on the market which have a value of 500 units to 

 the cubic centimeter. It is difficult to immunize 

 above this point. 



In some cases it is desirable to concentrate the 

 antitoxic serum. 



Gibson has devised a means for this depending 

 on the fact that the antitoxin is closely associated 

 with or comprises the globulin of the serum. The 

 method is as follows: 



To from 10 to 15 liters of serum, a saturated 

 solution of ammonium sulphate is added gradually 

 until precipitation is complete. This filtrate is 

 then removed by filtration through paper and 

 dissolved in 12 liters of water. It is then strained 

 through gauze to remove the filter paper. The 

 solution is reprecipitated with ammonium sulphate 

 and the precipitate removed as before. The 

 precipitate is then dissolved in 24 liters of a 

 saturated solution of sodium chlorid and filtered 

 through gauze. This solution is allowed to stand 

 over night and the supernatant fluid removed from 

 any precipitate which forms. The precipitate is 

 washed with saturated sodium chlorid and the 

 washing added to the first solution. 



The combined solutions are again precipitated 

 with saturated ammonium sulphate solution and 



