PRACTICAL APPLICATIONS 393 



great potency, as determined by its power of agglutination, which 

 may be manifested when it is diluted a million times. But the 

 immunity it confers (judging from laboratory experiments and 

 analogy with other diseases) is but temporary, and the method 

 can only be of occasional value. 



The plan of injecting the serum and vaccine in combination 

 suggested by Besredka is more promising. It is carried out as 

 follows : A twenty-four-hour agar culture of bacilli is mixed with 

 typhoid serum and incubated at 37 C. for twenty-four hours. 

 The bacilli are, of course, agglutinated, and the mass is washed 

 free from serum by repeated centrifugalizations with sterile 

 normal saline solution. The bacilli are then suspended in this 

 solution and heated to 60 C. for one hour. This vaccine is said 

 to produce very rapid immunity, with practically no negative 

 phase, and the local and general reactions it produces are but 

 slight. It has not yet been tested on a large scale. 



Simultaneous injections of serum and vaccine have also been 

 employed by Calrpette and others. The results do not appear to 

 be as satisfactory as those obtained from the use of the vaccine 

 alone. 



Bacillus Coli. 



The Bacillus coli, in addition to its haemolysin (colilysin) already 

 mentioned, produces an endotoxin, on which its pathogenic action 

 doubtless depends. Its vaccine is moderately toxic, causing 

 severe local irritation and general febrile reaction if the initial 

 dose be a large one. Filtrates from broth cultures are practically 

 devoid of toxicity. 



In regard to its immunity reactions B. coli closely resembles 

 B. typhosus. Bacteriolytic and opsonic substances are developed 

 during the course of the disease, and in both cases the opsonic 

 index must be estimated by the dilution method, Wright's original 

 process giving inaccurate results. There is some difference with 

 regard to the production of the agglutination reaction, which is 

 invariably present in typhoid infections, except in those acute 

 cases of the disease in which the patient dies before it has time to 

 develop. In infections with B. coli this is not the case, and in 

 many of the local infections, such as cystitis, pyelitis, etc,, no 

 appreciable agglutinative properties are developed. When animals 

 are immunized with massive doses extremely powerful clumping 

 sera are obtained, but this is not always observed in the treatment 

 of the human patient with vaccines. 



