PRACTICAL APPLICATION 253 



amounts of preservative. Delinquencies are reported immediately, and 

 steps are taken to withdraw that particular lot of serum from the market. 



A unit of diphtheria antitoxin may be defined as the "amount of anti- 

 toxin that mil just neutralize 100 minimal fatal doses of toxin for a 250- 

 gram guinea-pig." 



A unit of tetanus antitoxin may be defined as the "amount of antitoxin 

 which will just neutralize 1000 minimal fatal doses of toxin for a 350- 

 gram guinea-pig." 



The standardization of these serums is useful as a guide to their ad- 

 ministration, especially when given for prophylactic purposes, where 

 experience has taught that so many units usually confer protection; it 

 also serves for purposes of record. In the treatment of diphtheria and 

 tetanus, however, the serums are usually given until a therapeutic effect 

 is noted, regardless of the number of units administered. If it were 

 possible to determine quickly and accurately the amount of toxin in a 

 given patient, then neutralization could be accomplished along the same 

 lines that make this possible in the test-tube. The indications are to 

 administer at once sufficient antitoxin to neutralize all the toxin, giving 

 subsequent doses large enough to overcome the toxin as it is produced 

 until the focus of infection is removed. 



Antitoxin should be kept in a cold place and protected from air and 

 light. When this is done, they usually do not deteriorate more than 30 

 per cent, of their original strength, and often much less, within a year. 

 All manufacturers place a larger number of units in the container than 

 the label calls for, in this way allowing for the gradual loss in strength up 

 to the date specified on the label. According to Park, the antitoxin in 

 old serum is just as effective as that in fresh serum, except that there is 

 less of it. 



PRACTICAL APPLICATION 



The employment of antitoxic serums both in prophylaxis and in the 

 treatment of infection, is considered in greater detail in the chapter on 

 Passive Immunization and Serum Therapy. 



