PRACTICAL APPLICATIONS 389 



potent in this respect. The bacteriolytic power of the blood as 

 tested by Wright's method does not necessarily show a great 

 increase ; this is due probably to the lack of complement, and it is 

 possible that relapses may be due to the same cause, deviation of 

 complement occurring owing to the excess of immune body. 



There is, however, no doubt that phagocytosis plays a part of the 

 utmost importance in the natural cure of the disease, and that the 

 opsonic content of the blood (as tested by one of the dilution 

 methods) undergoes a steady rise during the process of immuniza- 

 tion. We may regard the mechanism by which the infection is 

 combated as a double one, bacteriolysis and phagocytosis being 

 jointly concerned. That the latter is of chief importance appears 

 probable, from the fact that typhoid bacilli set free their endotoxin 

 when dissolved by means of bacteriolytic sera. 



The antitoxin or anti-endotoxin of typhoid bacilli can be readily 

 prepared from animals by a process (somewhat prolonged) of 

 immunization with the endotoxin, prepared either by grinding the 

 bacilli, by dissolving them in bacteriolytic sera, or by allowing 

 them to undergo aseptic autolysis. There is, however, no proof 

 for the belief that this substance is developed during the natural 

 process of cure, or that it is a cause of the subsequent immunity. 

 It is quite as possible that the cessation of the febrile process 

 is due to the destruction of the bacilli, and consequent cessation 

 of the supply of toxin. 



The effect of the true typhoid toxin is seen during the earlier 

 stages of the disease, when the temperature is continuous. The 

 intermittent temperature of the later stages is probably due in 

 part to the absorption of other toxins from the ulcerated surfaces 

 of the Peyer's patches, and in part to the liberation of endotoxins 

 which occurs when bacilli are dissolved before being ingested. 



The duration of the immunity after a natural attack of the 

 disease is not accurately determined, but it is certainly long 

 perhaps several years. That due to preventive inoculation is 

 thought to be six months at least, but here again exact figures 

 cannot be obtained. The duration of the antibodies produced in 

 typhoid fever varies. The agglutinins usually disappear within 

 one or two years, but they may persist for seven or more. The 

 bacteriolysin is thought to go sooner, but the observations on 

 which this idea is based were mostly on the bactericidal powers 

 of the blood, and open to fallacy. 



Diagnosis. Usually the W 7 idal reaction is all that is required. 



