ACTIVE IMMUNITY BY FEEDING 559 



(Wright and Semple) (p. 375) ; (6) Pasteur's method of inocula- 

 tion against hydrophobia, which involves essentially , the same 

 principles (p. 618). 



Vaccines as a Method of Treatment. — Within recent years the 

 principles of active immunity have been directly applied in the 

 treatment of already existing disease. This is largely due to the 

 work of Wright, who, from his study of the part played by 

 phagocytosis in the successful combat of bacteria by the tissues, 

 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 view is that while 

 the local capacities of resistance may have been lowered, resisting 

 mechanisms in ■ other parts of the body have not been brought 

 into play. The vaccine may thus stimulate these, and the focus 

 of bacterial growth may be flooded with antibacterial bodies. 

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

 p. 130 ; the general principles supposed to underlie their use have 

 been discussed in connection with tuberculosis, p. 296.) Vaccines 

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

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

 b. coli, infections of joints by the gonococcus, and in many cases 

 considerable success has followed the treatment. Favourable 

 results have also been recorded in the case of more general 

 infections, such as ulcerative endocarditis, septicaemia, typhoid 

 fever, etc. In such cases it is stated that the best results are 

 obtained from the use of sensitised vaccines {vide supra). These 

 are prepared by subjecting living cultures (preferably of auto- 

 genous strains) to the action of say 5 c.c. of the appropriate 

 anti-serum for three hours at 37° C. The sensitised bacteria 

 are deposited by centrifuging, emulsified in saline containing - 5 

 per cent, phenol, and again kept at 37° C. for three hours, so 

 that the phenol may kill them. The vaccine is then ready for 

 use. In infections with streptococci or the b. coli from ten to 

 forty millions may be given, the dose being repeated in twenty- 

 four hours. In very acute infections a few hundred thousand 

 sensitised bacteria may produce definite results, and if improve- 

 ment of symptoms occurs the dose may be cautiously repeated in 

 six hours. 



Active Immunity by Feeding. — Ehrlich found that mice 

 could be gradually immunised against ricin and abrin by feeding 

 them with increasing quantities of these substances (vide p. 193). 



