434 PATHOGENIC MICROORGANISMS 



a P H of 7.2. The organisms arc then centrifugcd down, arc washed 

 once or twice in the stock broth of a P H of 7.4 prepared as above. 

 They are then resuspended in the same medium in approximately 

 the original concentration of the culture, and this suspension is used 

 for agglutination. This method has given sufficiently reliable results, 

 and, although we have tried a great many other procedures, such 

 as grinding the organisms in salt, shaking them for long periods, 

 etc., we have not been able to obtain homogeneous mixtures better 

 adapted for agglutination tests. For the present we would recom- 

 mend the method of Dochez and Avery as perhaps the most useful, 

 but it cannot be regarded as entirely satisfactory as yet. (For 

 preparation of the medium see chapter on media.) 



Passive therapeutic immunization with polyvalent antistrepto- 

 coccus serum has not yet given reliable results. In view of the 

 i recent work on pneumococcus sera we believe it should be subjected 

 to careful clinical trial especially in cases of spreading cellulitis and 

 streptococcus pneumonias and empyemas which do not yield to the 

 ordinary forms of treatment. 



THE PROBLEM OF MUTATION 



The many minor differences in morphology and cultural char- 

 acteristics which have been noticed among the streptococci have 

 lead to many assumptions of possible mutations in this group. It 

 is, of course, well known that changes in the length of chains in 

 the production of green color by viridans strains, and the degree 

 of hemolysis can be observed in streptococci grown in the laboratory 

 for a long time. These changes, however, may 4)e regarded as 

 analogous to minor changes produced under conditions of artificial 

 cultivation in many other groups, such as the typhoid bacilli and others, 

 but do not imply a fundamental change or true mutation. Burger and 

 Wyntenberg 105 claimed that passage through white mice converted 

 a capsulated hemolytic streptococcus into what they took to be a 

 pneumococcus. Rosenow 106 has been the most prominent worker 

 along these lines, and in 1912 claimed that he had transformed a 

 capsulated streptococcus into a typical streptococcus by cultivation 



105 Burger and Wyntenberg, Jour. Infec. Dis., 4, 1907, 609. 

 Rosenow, Jour. Infec, Dis., 14, 1914, 1. 



