240 ANTITOXINS 



lins. The use of concentrated serum has lessened the incidence of serum 

 sickness and facilitates the administration of large doses. Briefly /'the 

 method of Banzhaf is as follows: "The citrated plasma is diluted with 

 half its volume of water and saturated ammonium sulphate solution is 

 added up to 30 per cent, saturated solution. This mixture is heated up 

 to 60 C. and held there for one hour. Then filtered while hot. The 

 precipate contains the native non-antitoxic proteins and a large amount 

 of non-antitoxic proteins newly formed by the above method of heating. 

 This precipitate is discarded. The nitrate is brought up to 50 per cent, 

 saturated ammonium sulphate solution. The resulting precipitate 

 contains only pseudoglobulin and antitoxin and is pressed to remove 

 excess of fluid, followed by dialyzation until free from salts. After 

 dialysis is completed 0.8 per cent, sodium chlorid is added for isotox- 

 icity and 0.3 per cent, tricresol for preservation. It is then filtered 

 through paper pulp and a Berkefeld clay filter, tested for sterility and 

 potency, and filled into sterile syringes or bottles. This method gives a 

 concentration of about six times the original potency" (Park). 



Standardizing the Serum. During the earlier investigations it was 

 believed that toxin was quite stable, and that it possessed a definite 

 toxicity with a constant value in neutralizing antitoxin. Upon these 

 suppositions the original Behring-Ehrlich antitoxin unit was based, 

 consisting of 10 times the amount of antitoxin that neutralized 10 fatal 

 doses of toxin. For example, if the minimal lethal dose (M. L. D.) of 

 toxin was 0.001 c.c., and 0.01 c.c. was neutralized by 0.01 c.c. of serum, 

 then 0.1 c.c. of serum equaled' one unit, or 10 units in a cubic centimeter. 

 Later stronger serums were found, and von Behring and Ehrlich modi- 

 fied the unit, which they now call the immunity unit, to be that quantity 

 of antitoxin which will neutralize 100 times the minimal fatal dose for a 

 250-gram guinea-pig. 



It was soon discovered that toxins are unstable compounds, and that, 

 almost immediately after their production, they begin to change into 

 toxoids, which are not acutely poisonous, but which retain their power 

 to neutralize antitoxin. 



In order to standardize a serum it is necessary that the strength of 

 the toxin be known, and since this is so variable, a standard antitoxin is 

 supplied by the Hygienic Laboratory, by which the various antitoxin 

 plants may measure the strength of their toxins. By mixing varying 

 quantities of toxin with one unit of this standard antitoxin and injecting 

 these into 250-gram guinea-pigs, the L + (limes death) dose is obtained, 

 which is the dose of toxin required to kill a pig in four days with the one 



