768 PASSIVE IMMUNIZATION SERUM THERAPY 



individual in case virulent bacilli should be inspired or otherwise gain 

 access to the tissues. 



The doses advised are relatively small, and the injection does not 

 usually produce any discomfort other than soreness about the site of in- 

 oculation. For infants under one year of age 500 units suffice; for 

 older children and adults from 1000 to 1500 units should be given. 



The duration of this passive immunity is relatively short, owing to the 

 fact that the antitoxin is eliminated rapidly, as it is part and parcel of a 

 foreign serum that tends to be excreted or destroyed soon after its intro- 

 duction into the body. It will endure, however, for at least two weeks, 

 and frequently longer. Since the incubation period of diphtheria is 

 only a matter of a few days, this suffices, in the majority of instances, to 

 protect the individual. 



The indications are to immunize all persons who have come in inti- 

 mate contact with a case of diphtheria. If time permits the Schick test 

 should be conducted, as only those persons yielding positive reactions 

 require the -antitoxin (see page 229). It is especially valuable in fam- 

 ilies and small communities, such as go to make up hospital wards 

 and asylums. The physician who is attending a case of diphtheria in 

 a private home should urge immunization upon all members of the house- 

 hold. 



The immediate results ?,re usually good. The main disadvantage is 

 the short duration of the immunity, so that no matter how faithfully it 

 is carried out, persons do not remain immune for long periods of time, 

 and accordingly the total morbidity of the disease is not influenced to 

 any extent. In homes from which the case of diphtheria is promptly 

 removed to a special contagious hospital and in which the remaining 

 members are promptly immunized the percentage of secondary cases 

 is practically nil. Of 6772 patients who were removed to the Phila- 

 delphia Hospital for Contagious Diseases, the remaining members of 

 the family not being immunized, secondary cases developed in 164 per- 

 sons, or in 2.4 per cent. Of 4063 cases of diphtheria treated at home with 

 antitoxin, the other members of the family not being immunized, sec- 

 ondary cases developed in 219 persons, or in 5.3 per cent. Of 639 diph- 

 theric patients treated at home who did not receive antitoxin and where 

 immunization was not practised, secondary cases developed in 151 

 persons, or 23.6 per cent. These figures, compiled by Dr. A. A. Cairns, 

 chief medical inspector of Philadelphia, and taken from the annual re- 

 ports of the Philadelphia Bureau of Health for the years of 1909, 1910, 

 and 1911, show that the best results are obtained when the diphtheric 



