394 APPLICATION OF METHODS OP BACTERIOLOGY 



protective bodies are to be demonstrated at all; in the ma- 

 jority of cases a certain amount of such protective agents is 

 to be demonstrated. In some cases protective bodies may 

 be detected in the blood a few hours after the crisis, and 

 none may be found a few days later. It is such inconstancies 

 as these that call into question the explanation offered 

 above, or at least justify the suspicion that the crisis may 

 be dependent upon other factors in addition to those having 

 to do with the neutralization of poison or the destruction 

 of a certain number of the germs. 



It has been suggested that such other factors may com- 

 prise provisions for preventing further growth of the pneu- 

 mococci in the tissues without actually killing them or 

 robbing them of their power to produce infection when 

 removed alive from the pneumonic patient. 



It also has been suggested that the crisis constitutes the 

 advent of a refractory state on the part of the tissues — a 

 state having some analogies to anaphylactic shock. As 

 yet this can be taken only as a suggestion. Much more in 

 the way of experimental evidence is needed before it can 

 be accepted. 



It is scarcely suitable to a book of this character to pursue 

 all the lines of argument that have been advanced in con- 

 nection with this subject. It suffices to say that at present 

 we are forced still to speculate as to the nature of at least 

 some of the important factors responsible for the self limi- 

 tation of this desease. 



Immunization and Specific Antisera. — ^Little difficulty has 

 been experienced in the efforts to actively immunize animals 

 from pneumococcus infection. Horses have been carried 

 to such a high degree of immunization by repeated intra- 

 venous injection of pneumococcus cultures that as much as 



