474 PATHOGENIC MICROORGANISMS 



the upper respiratory passages could not, in itself, produce pneumonia, 

 and that when the disease occurred, it was in most cases due to auto- 

 infection, owing to unusual depression of resistance in an individual 

 in whose mouth the pneumococcus happened to be present. Moreover, 

 there seemed to be many instances of relationship between unusual 

 exposure to cold and wet, and the occurrence of pneumonia, while it 

 was rarely possible to trace definitely the origin of a case to exposure 

 to a previous one. 



Recent recognition that there are a number of different types of 

 pneumococci, investigations which were begun by Neufeld and 

 Haendel, 89 and followed out more particularly in this country by 

 Dochez and Avery, 90 has furnished us with an entirely new set of 

 facts for the understanding of pneumonia epidemics. The types of 

 pneumococci, as worked out by these writers, have been tabulated in 

 another place. This tentative subdivision into types has made it 

 possible to determine, in the first place, whether or not the ordinary 

 mouth types are identical with those found in the lungs during pneu- 

 monia, and have also permitted us to determine whether the type 

 present in any particular case was identical with that found in a pre- 

 ceding case or in a closely associated contact. Following up this trail, 

 workers at the Rockefeller Hospital have found that over 50 per cent 

 of the mouth organisms found in normal human beings in and about 

 New York city belong to the heterogeneous type IV group, whereas, 

 over 80 per cent of lobar pneumonias are due to types I, II, and III. 

 The obvious inference from this reversed percentage is that lobar 

 pneumonia is in most cases caused by organisms transmitted to the 

 victim from an extraneous source, and that autoinfection with the 

 patient's own mouth organisms cannot be regarded as a very common 

 occurrence. 



It should not be concluded from this, however, that type IV is 

 unimportant as a causative agent in the disease, since the more recent 

 statistics gathered during the war show that a considerable percentage 

 of cases in different localities may be caused by this group. However, 

 since this group is composed of many apparently unrelated members, 

 we can not obtain further light upon the epidemiological conditions, 

 under such circumstances, at the present time. 



It has also been shown bv Stillmair 11 and others that the more 



"Ncufcld :IIM| Ihu'Hdcl, Arb. a. <1. k. Gsmlhtsamte, 1010, 34, 293. 



30 Doclicz and Avery, Proc. Soc., Expcr. Med. and Biol., 14, 1916-37, 126. 



91 Stillman, Jour. Exper. Med., 26, 1917, 513. 



