BACILLI OF THE COLON-TYPHOID-DYSENTERY GROUP 667 



which is supposed to increase agglutinability. After this, it is planted 

 in flasks in broth, allowed to grow overnight, and 0.1 per cent formalin 

 is added. 09 This formalinized culture is placed in the refrigerator and 

 shaken frequently during four or five days. It is then standardized 

 for opacity against an arbitrary standard kept on hand, and prepared 

 in the Army Medical School. Necessary dilutions are made with 

 physiological salt solution to which 0.1 per cent formalin has been 

 added. 



The suspension is then standardized for agglutinability against a 

 known agglutinating immune serum. For this purpose incubation at 

 55 for two hours is a method used for the final reading. It is easy, 

 from this test, then, to determine the agglutinability factor of the new 

 suspension. 



The example cited in the Army Medical School War Manual, No. 6, 

 is as follows: If the dilution of the solution in which the standardized 

 suspension is agglutinated is 1 to 6400, while that of the new suspension 

 is 1 to 3200, then the factor of the new bacterial suspension is one-half. 



By the use of such suspension it is clear that comparative titrations 

 of the rise and fall of agglutinins in the patient's serum can be made, 

 and information obtained which may have considerable importance in 

 deciding whether the appearance of agglutinins in the patient is due 

 to previous vaccination, or is present in response to a fresh infection. 



Precipitins. The investigations of Kraus, 70 by which the pre- 

 cipitins were discovered, revealed specific precipitating substances, 

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

 investigation, these substances have been studied by Norris 71 and 

 others. 72 



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 intracellularly, after ingestion by the leucocytes. 

 Klein 73 has attempted to overcome this difficulty by working with 

 dilutions of serum, at the same time using comparatively thick 

 bacterial emulsions and exposures to the phagocytic action not exceed- 



69 U. S. Medical War Manual No. 6. Lea & Febiger, 1919. 



70 Kraus, Wien. klin. Woch., xxxii, 1897. 



71 Norris, Jour, of Inf. Dis., I, 3, 1904. 



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



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



