110 VACCINE AND SERUM THERAPY. 



fore they have had sufficient chance for multiplication and pro- 

 duct ion of poisons which kill the cells in the body. For this reason 

 anti-bacterial sera are frequently called bactericidal sera. In 

 the serum of individuals and animals that have acquired anti- 

 bacterial immunity, various kinds of anti -bodies are found. The 

 best known of these bodies are bacteriolysins, opsonins, precipi- 

 tins and agglutinins. These prepared anti-bodies are introduced 

 into the body in passive immunization. The importance and 

 value in immunity of all of these anti-bodies is not known, but it 

 is generally accepted that agglutinins and precipitins are of little 

 or no value, while opsonins and bacteriolysins are considered of 

 importance in anti -bacterial immunity. Bacteriolytic immune sera 

 depend for their action on specific substances called ' 'bacteriolysins, ' ' 

 which dissolve bacteria. The value of opsonins in bactericidal 

 sera to be used in injections for the purposes of conferring passive 

 immunity, is still indefinitely understood, although some investi- 

 gators have attached considerable importance to their presence 

 in sera. 



The anti -bodies in anti -sera called agglutinins and precipi- 

 tins belong to the second order of receptors, the bacteriolysins 

 to the third order, while in regard to opsonins, no statement can 

 be made at the present time some regarding them as belonging 

 to the second and others to the third order of receptors. 



Anti-sera containing receptors of either the second or third 

 order are easily inactivated by heat, age, acids, etc. After inacti- 

 vation they are no longer able to produce agglutination, precipi- 

 tation, lysis, or opsonification. The loss of power to produce these 

 effects depends on the destruction of ferment -like substances, which 

 are a part of the agglutinin and precipitin receptors and are fur- 

 nished to the receptors of the third order by the fresh blood serum. 

 (See page 18.) Inactivated bacteriolytic serum differs from in- 

 activated or aged agglutinating or precipitating serum in that 

 on the addition of fresh serum the anti -bodies producing lysis 

 can be re-activated, while the agglutinating and precipitating 

 properties cannot be restored in this way. Because the different 

 specific bacteriolytic sera used in passive immunization are usually 

 not freshly drawn and therefore have been inactivated by age, 

 the individual or animal immunized must furnish the complement 

 or ferment-like substance so as to make the destruction of bacteria 



