BY BACTERIAL PRODUCTS OR TOXINS 519 



principles of active immunity had not been directly applied in 

 the treatment of an existing disease except in the case of tuber- 

 culosis. The work of Wright, however, shows that active 

 immunisation in such circumstances is not only possible, but is 

 also probably capable of wide application. From his study of 

 the part played by phagocytosis in the successful combat of 

 bacteria by the body, he was led to advocate the treatment 

 of bacterial infections by carrying on an active immunisation 

 against the causal agents by the injection of dead cultures of 

 the latter. The justification for such a procedure lies in his 

 contention that in many cases infections are to be looked on as 

 practically localised, e.g. the cases of an acne pustule, or a boil. 

 The reason for the local growth of bacteria in the part of the 

 body affected is that there is for unknown causes a deficiency 

 of the opsonic power (vide p. 291) of the body fluids, which is 

 essential for the phagocytosis of the invading bacteria. Still 

 more marked in such cases is the deficiency in the opsonic 

 qualities of the fluids in the actual site of infection. Any 

 procedure which will raise the opsonic power of the body fluids 

 M ;i whole, and therefore of the fluids in the focus of infection, 

 will aid the destruction of the bacteria by sensitising them to 

 phagocytic action. Such a procedure is found in the active 

 immunisation which results from the injection of a vaccine 

 consisting of a dead culture of the causal bacteria. The 

 application of a vaccine of this kind can be controlled by 

 observation of the opsonic index of the patient's serum during 

 the treatment. When a local infection is present the general 

 opsonic index is usually found to be below unity. If dead 

 bacteria be injected into the individual there may occur during 

 the following few days a further fall in the opsonic index, 

 what Wright calls the occurrence of a negative phase. In a case 

 where the treatment is successful, this negative phase is succeeded 

 by a rise in the opsonic index above its original level, occurrence 

 of positive phase, and with this reaction there is an improve- 

 ment in the local condition. Usually in such cases repeated 

 injections are required to effect a cure, and the important point, 

 according to Wright, is to avoid giving an injection when a 

 negative phase is in progress. If this point is not attended to 

 an aggravation of symptoms may occur (vide p. 291). 

 With regard to the details of the preparation of the vaccines see 

 p. 133. The number of bacteria employed for a vaccination 

 varies from 5,000,000 to 500,000,000 or more. Such vaccines 

 have been used extensively in the treatment of acne, boils, 

 sycosis, tuberculosis, infections of the genito-urinary tract by the 



