344 APPLICATION OF METHODS OF BACTERIOLOGY 



possessing all the common characteristics of the type species, 

 reveal greater or less individual modification in some one 

 or another functional particular. When such modification 

 occurs in pathogenic power, or in some other essential 

 function, as is often the case, it is probable that they may 

 have an effect upon the results of immunization. At all 

 events experience with the serum of animals immunized 

 from closely allied though not identical varieties of a species 

 obtained from various lesions, warrant this opinion. For 

 instance: given Streptococcus A, B and C, obtained from 

 different sources, there is no assurance that the serum of 

 an animal immunized from strain A will necessarily act 

 favorably in an infection caused by B or C, even though its 

 action in infection caused by A may be entirely satisfactory, 

 and vice versa. This experiment has led to the general 

 conclusion that for favorable therapeutic action on the part 

 of an antiserum it is advisable that such serum be obtained 

 from animals immunized from the particular strain of 

 infective organism that is concerned in the disease for which 

 the serum is to be used in treatment. 



This does not necessarily imply that the particular culture 

 obtained from each of the manifold pathological lesions 

 shall be used as the immunizing agent in efforts to secure an 

 antiserum for the pathological condition from which it 

 was derived, but rather suggests the desirability of estab- 

 lishing, through culture or other tests, sub-groups having 

 more or less common peculiarities so that even though the 

 members of group A may differ slightly in details from one 

 another, such difference is nevertheless much less than that 

 observed between themselves and the members of group 

 B or C, and an antiserum produced through the use of 

 either of the members of group A will act favorably upon 



