238 PASSIVE IMMUNIZATION 



gave 4000 to 5000 units every five days for four weeks in severe 

 cases. At the Berlin Charite four-fifths of the cases require from 

 1500 to 4500 units; in the remainder 9000 to 18,000 are common 

 amounts, and in the severest cases 30,000 to 65,000 have been used. 

 Above all, then, the physician should not despair in the face of a 

 grave case, but use the antitoxin systematically until the child is 

 either dead or out of danger. The same rule applies in the man- 

 agement of those cases in which post-diphtheritic paralyses have 

 occurred. In the past it was thought that antitoxin would be of 

 no avail in suqh cases, but in the light of more recent experience it 

 would seem that here also much good may come from the systematic 

 use of the serum. 



The question, of course, suggests itself, why antitoxin should still 

 be of service when once the toxin has been anchored to sensitive 

 receptors; but I would recall that as a consequence of immunization, 

 the specificity of the receptors for the corresponding antigen may be 

 very materially increased and that the toxin in question will hence 

 have a greater affinity for the antitoxin furnished by the horse 

 than for the sessile receptors of the patient. Hence, the possibility 

 exists, theoretically at least, that an active antitoxin may be able to 

 break the combination between the toxin and the patient's recep- 

 tors, and our clinical experience suggests that this actually occurs. 

 To effect this end, however, large doses are evidently necessary. 



Prophylactic Dose. For prophylactic purposes a dose of from 

 500 to 1000 units has been found sufficient to afford protection for 

 approximately three weeks. Whether or not this period could be 

 lengthened by the administration of larger amounts seems doubtful, 

 in view of the fact that the drop in the blood content of antitoxin 

 which takes place within the first few days of its injection is the 

 more abrupt the larger the dose. This will be understood if we bear 

 in mind that the antitoxic properties of horse serum are intimately 

 connected with its globulins, and that these are alien albumins which 

 the body cannot utilize as such and which it accordingly tries to 

 destroy as soon as possible. 



In connection with the question of prophylactic immunization 

 it is interesting to note that recent investigations have demonstrated 

 that whereas the blood of children affected with diphtheria is devoid 

 of any antitoxin before injection a very large percentage of indi- 

 viduals free from diphtheria is naturally protected, viz., 40 per cent. 



