578 MICROBIOLOGY OF SPECIAL INDUSTRIES 



mixed with the L+ dose of diphtheria toxin and injected into a series 

 of guinea-pigs, each weighing 250 ^. * The L-f- dose of toxin is the least 

 amount of toxin, which, when mixed with one unit of standard antitoxin 

 (suppUed by the Hygienic Laboratory) and injected into a guinea-pig 

 of 250 g. weight, is suflGicient to kill the animal in four days. From the 

 results of this test it is. possible to determine the smallest amount. of the 

 antitoxin which will protect a, guinea-pig of 250 g. weight, when the 

 animal has received simultaneously the L-|- dose of toxin. This mini- 

 mum amount of antitoxin represents one unit. Thus, if J^oo c-C- of the 

 given antitoxin represents the smallest amount which is capable pf 

 neutralizing the L-f- dose of toxin, then the antitoxin would possess a 

 potency gi 500 units per c.c. 



In order that the antitoxin may be tested for safety, each of several 

 guinea-pigs is injected subcutaneously with about 2 c.c. of the serum. 

 These animals are not released until the observer is satisfied that the 

 serum contains no injurious properties. For the purpose of detection 

 of microbial contamination, relatively large amounts of the antitoxin 

 are placed in culture media and incubated under both aerobic and 

 anaerobic conditions. 



Diphtheria antitoxin is usually distributed in glass syringe containers 

 ready for immediate use. After the product has been tested relative 

 to potency, safety and microbial contamination, it is put up in sterile 

 glass cyUnders. These cyhnders are so constructed that accompanying 

 sterilized needles and pistons may be conveniently applied and the anti- 

 toxin injected hypodermicaUy directly from the containers. Each 

 container must bear a label indicating the number of antitoxin units 

 enclosed, and the date of preparation. 



Finally, after the diphtheria antitoxin has been distributed in the 

 glass cylinders, sealed and packed ready for use, sample packages are 

 opened and examined for contamination, usually by two microbiologists. 

 The product is not approved until the independent results of these final 

 tests are compared, and it is assured that microbial contamination is 

 absent. ' 



All antitoxic serums should be kept away from the light and at a 

 temperature of 10° to 15° whenever possible, as the presence of heat 

 and light causes gradual deterioration. Usually an expiration date of 

 from eighteen months to two years is applied to diphtheria antitoxin. 



* See Bulletin No. 2i, Hygienic Laboratory, Washington, D.C., 



