PRODUCTION OF ANTITOXINS FOR THERAPEUTIC PURPOSES 239 



tinue to furnish blood containing the maximum amount of antitoxin 

 for several months, and then, in spite of increasing injections of toxin, 

 begin to furnish blood of gradually decreasing strength. If an interval 

 of three months' freedom from inoculation is allowed once every nine 

 months, the best horses will furnish high-grade serum for from two to 

 four years. 



Collecting the Serum. In order to obtain the serum, the neck of 

 the horse should be cleansed thoroughly as for an aseptic operation, and 

 a special tourniquet applied to distend the jugular vein. A small slit 

 is made through the skin over the vein, and a special sharp-pointed 

 cannula is passed upward under the skin for two inches or more and 

 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. 73) 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. 



Method of Concentrating Serum by Isolating the Antitoxin Globu- 



