424 PATHOGENIC MICROORGANISMS 



precipitins were discovered, revealed specific precipitating substances, 

 among others, also in typhoid immune sera. Since Kraus' original in- 

 vestigation, these substances have been studied by Norris * and others. 2 



Opsonins. A number of observers have shown that opsonins specific 

 for the typhoid bacillus are formed in animals immunized with these 

 organisms. Opsonins are formed also in patients suffering from typhoid 

 fever, but exact opsonic estimations in all these cases are extremely 

 difficult because of the rapid lysis which these bacteria may undergo 

 both in the serum, and intracelluiarly after ingestion by the leucocytes. 

 Klein 3 has attempted in part to overcome this difficulty by working 

 with dilutions of serum and at the same time using comparatively thick 

 bacterial emulsions and exposures to the phagocytic action not exceed- 

 ing ten minutes. Chantemesse 4 has claimed that the opsonic index of 

 typhoid patients was increased after treatment with a serum obtained 

 by him from immunized horses, and Harrison 5 has reported similar 

 results in patients treated by a modification of Wright's method of 

 active immunization. Klein claims to have demonstrated that in 

 typhoid-immune rabbits, after five- injections, the opsonic contents of 

 the blood were increased to an equal extent with the bactericidal sub- 

 stances. He concludes from this interesting observation that it may 

 well be that the opsonins are quite as important in typhoid immunity 

 as are the latter substances. 



For diagnostic purposes in typhoid fever the estimation of the opsonic 

 index, so far, has not been proven to be of great value. 



Specific Therapy in Typhoid Fever. The failure to produce a soluble 

 toxin from typhoid cultures has naturally so far precluded the possibility 

 of an antitoxic therapy, such as that which has been successful in diph- 

 theria. In the light of our present knowledge of the poisonous products 

 of the typhoid bacillus it seems but natural that attempts by earlier 

 investigators to apply the principles of Behririg's work to typhoid fever 

 were doomed to fail. Attempts to employ specific bactericidal and bac- 

 teriolytic sera for therapeutic purposes in this disease have also been 

 without favorable result. 



Active Prophylactic Immunization. We have seen that work by 

 Pfeiffer and Kolle and later by many others has shown that it is com- 



1 Narris, Jour, of Inf. Dis., I, 3, 1904. 



2 Barker and Cole, 22d Ann. Session, Assn. of Amer. Phys., Wash., 1897. 



3 Klein, Bull. Johns Hopkins Hosp., 1907. 



* Chantemesse, 14th Internatl. Cong, for Hyg., Berlin, 1907. 

 6 Harrison, Jour. Royal Army Med. Corps, 8, 1907. 



