316 AGEICULTUEAL AND INDUSTKIAL BACTEEIOLOGY 



for each are so specific that they will not immunize against 

 other strains. Immunization against streptococcus infec- 

 tions by the use of vaccine, consisting of suspensions of 

 killed streptococci, has been frequently attempted. "While 

 some favorable results have been reported, the results on the 

 whole do not appear to be particularly encouraging unless 

 great care is taken that the organisms injected are the ones 

 against which immunity is actually desired. So-called 

 autogenic vaccines have been used with some degree of suc- 

 cess in chronic infections. In chronic erysipelas, for ex- 

 ample, there are reports of favorable results secured by 

 injecting dead cultures of the type of organism causing the 

 infection in the particular individual to be protected. 

 Streptococci are common constituents of many of the so- 

 called influenza vaccines, inasmuch as the streptococci have 

 been found in many instances to produce the post-influenza 

 pneumonias. 



Vaccines against streptococcus infections have been pre- 

 pared in a variety of ways. Todd made such a vaccine by 

 first growing the streptococci on blood serum for twenty- 

 four hours, and inoculating from these cultures into large 

 flasks containing ten per cent serum broth. These were 

 incubated for one month. Six per cent of sterile glycerin 

 is added and this material concentrated at 60° C. for two 

 days over unslaked lime. It is evident that the thick paste 

 thus secured is made up of the products of autolysis of 

 the bacteria, as well as the growth products and unchanged 

 serum broth. It is diluted before use as a vaccine. Other 

 investigators have prepared bacterial extracts by shaking 

 broth cultures either with urea or galactose in twenty-five 

 per cent solution for several days. The high concentration 

 of the solution tends to destroy the organisms, and the 

 shaking to disintegrate them. The vaccine is thereby 

 rendered sterile without heat, and the antigen, therefore, 

 is not altered. 



