PRODUCTION OF ANTITOXINS FOR THERAPEUTIC PURPOSES 231 



then plunged into the vein. From 6 to 12 liters of blood are collected 

 by a rubber tube into cylindric jars provided with special tops, facilitat- 

 ing filling with blood and subsequent withdrawal of the serum. The 

 cannula, tubing, jars, and everything used in collecting the blood and 

 serum should be carefully sterilized, and the whole operation should 

 be conducted with scrupulous aseptic care in order to avoid contamina- 

 tion. (See Fig. 26.) 



The jars are set aside (Fig. 70) for three or four days, and the serum 

 is drawn off by means of sterile glass and rubber tubing and stored in 

 large sterile bottles. When the globulins are to be separated, the blood 

 may be added directly to one-tenth of its volume of a 10 per cent, solu- 

 tion of sodium citrate, which prevents clotting of the blood. 



The serum should be clear and free from blood, and its sterility 

 should be proved by culture tests. An antiseptic, such as 0.4 per cent, 

 tricresol, 0.5 per cent, phenol, or chloroform, may be added, but this is 

 not necessary unless it is desired to keep the serum for some time. The 

 serum is poured into small bottles fitted with rubber stoppers, or placed 

 in special syringes labeled with the number of units contained. The 

 whole process should be conducted with scrupulous aseptic technic. 

 Diphtheria toxin varies too much to be used as a standard in determin- 

 ing the antitoxin content of a serum; hence a dried antitoxin is pre- 

 pared by the Hygienic Laboratory and is distributed for this purpose. 

 The serum is evaporated and dried in vacuo by passing dry sterile air 

 heated to 35 C. through it, and when perfectly dry, is preserved in 

 special containers over anhydrous phosphoric acid at a constant temper- 

 ature of 5 C. Preserved in this manner, the antitoxin is quite stable. 

 Just before use it is dissolved in the required amount of sterile normal 

 salt solution. 



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. 



