412 APPLICATION OF METHODS OF BACTERIOLOGY 



In other words, certain " types " of pneumococcus are 

 most common to this than to that expression of pneumonia 

 and are more or less identified with the varying fatalities 

 of the disease. 



At the present time, four types of pneumococci, dis- 

 tinguished from one another by specific agglutinating 

 reactions, are recognized and no transmutation from one 

 type to the other has been observed, even though every 

 experimental effort has been made to determine if such 

 occurs. 



Types. Type I pneumococcus causes between 30 and 50 

 per cent, of all true pneumonias and results in a fatality of 

 almost 25 per cent, of the cases with which it is associated. 



Type II pneumococcus causes from about 15 to 33 per 

 cent, of true pneumonias and is fatal to nearly 60 per cent, 

 of the cases in which it is found. 



Type III pneumococcus is present in from about 8 to 12 

 per cent, of lobar pneumonias. Its presence is associated 

 with a mortality in the neighborhood of 60 per cent. 



This type (III) is distinguished from the other types not 

 only by its specific agglutinating reactions, but by the 

 mucoid character of its growth under artificial conditions 

 and its tendency to develop into streptococcus-like chains. 



Type IV pneumococcus comprises a heterogeneous group 

 none of which can properly be included in either of the 

 other groups. In this group are found those pneumococci 

 so often present in the saliva of normal individuals and 

 which were regarded at one time as the specific exciters of 

 pneumonia. In morphology and general biological par- 

 ticulars the organisms in this group are alike, but by the 

 agglutinations test they are found to differ from one another 

 as well as from the other types. Etiologically, Type IV 



