SERUM ANTIDIPHTHERICUM 459 



of the vaccine. From 5 to 10 drops of the dilution which fails to produce 

 a definite skin reaction may be injected subcutaneously as the first dose. 

 Injections, increasing by a few drops at first, and later by the use of a 

 stronger dilution, may then be given at intervals of a few days or a week. 

 HAY FEVER VACCINE. A non-proprietary brand complying with the 

 standards for pollen extract. 



B. PASSIVE IMMUNIZATION 



The agents in passive immunity are called "antibodies" and they 

 directly antagonize the invading bacteria or toxin. These antibodies are 

 formed in the bodies of the larger domestic animals by active immuniza- 

 tion and when the antibacterial and antitoxic substances have reached a 

 high concentration the animal is bled and the serum saved. This serum 

 is injected into other animals and these latter immediately become endowed 

 with an increased resistance to the homologous infective agent. Unfortu- 

 nately, this protection is of short duration as contrasted to the more 

 permanent protection of active immunity. 



i. BY INJECTION OF ANTITOXINS. Toxins may be secreted by plants, 

 bacteria and animals, but the typical ones are of the tetanus and diphtheria 

 organisms. 



SERUM ANTIDIPHTHERICUM, U.S.P. A yellowish or yellowish- 

 brown transparent or slightly turbid liquid, with sometimes a slight granular 

 sediment; odorless, or having an odor due to the presence of an antiseptic 

 used as a preservative. Antidiphtheric serum gradually loses its potency, 

 the loss in one year varying between 10 and 30 per cent. The serum must 

 come from healthy animals, must be sterile, must be free from toxins or 

 other bacterial products, and must not contain an excessive amount of 

 preservative (not more than 0.5 per cent, of phenol, nor 0.4 per cent, of 

 cresol when either of these is used) and the total solids must not exceed 

 20 per cent. Serum of a lower potency than 250 units per mil must not 

 be sold or dispensed. Only such Sera may be sold as have been prepared 

 and propagated in establishments licensed by the Secretary of the Treasury 

 of the United States. The United States law requires that each container 

 of Serum sold by licensed establishments shall bear upon the label, in addi- 

 tion to the name of the Serum, the name, address and license number of 

 the manufacturer and the date beyond which the product cannot be ex- 

 pected to yield its specific results. The label must also contain the labora- 

 tory number of the Serum, the name and the percentage units claimed 

 for the contents of the container. The standard strength expressed in 

 units of antitoxic powder shall be that established by the United States 

 Public Health Service. 



This native antitoxin serum is little used in the United States, where 

 the methods of concentration have reached their highest development. 

 The potency of all diphtheria antitoxin sold in interstate commerce must 



