268 IMMUNOLOGY 



posed recently. In the treatment of diphtheria one large dose 

 should be administered as early in the disease as possible. This 

 is preferable to the administration of the same amount of anti- 

 toxin in divided doses. After toxin is bound to tissue, it is difficult 

 to neutralize. The function of antitoxin is to neutralize toxin; it 

 cannot restore injured tissue to normal nor destroy the diphtheria 

 bacillus. 



8. It has been ascertained by means of the Schick test that 

 the greatest percentage of susceptibility in a population occurs 

 in the children of preschool age. 



Toxin-antitoxin, Ramon toxoid, alum toxoid and alum precipi- 

 tated and resuspended toxoid are all used in active immuni- 

 zation against diphtheria. At the present time the antitoxin 

 present in toxin-antitoxin mixtures is obtained from goats. This 

 avoids the possibility of sensitizing an individual to horse proteins. 



Toxoid is apparently superior to toxin-antitoxin mixtures as an 

 immunizing agent. It has the additional advantage of not con- 

 taining serum protein of any kind. The Ramon toxoid gives 

 severe reactions in many older children and adults but seems to 

 be nontoxic for children under 8 years of age. Toxoid cannot 

 be used to determine susceptibility. 



The student should bear in mind that active immunity develops 

 slowly ; i.e., within three to six weeks and hence active immuni- 

 zation is of no value in treatment or immediate prophylaxis. 



Harrison reports that 64 per cent of the susceptible school chil- 

 dren of Washington were successfully immunized with toxin- 

 antitoxin. Park, on the other hand, reports that about 80 per 

 cent are successfully immunized by toxin-antitoxin. In some 

 series he has been even more successful, the percentage reaching 

 85 or even 90. It will be several years before one can say defi- 

 nitely how much better toxoid and treated toxoid are than toxin- 

 antitoxin. There is considerable evidence indicating that tlie best 

 immunizing agent is alum toxoid or precipitated toxoid, while 

 the Ramon toxoid is second and toxin-antitoxin third. The quality 

 of the preparation used, the dosage, number of doses, time 

 interval intervening between injections and also between the 

 first injection and the date of retesting are important factors to 

 be considered in evaluating data. Individuals who possess a 



