308 BACTERIOLOGY. 



forty cases, came to the following conclusions : 1. The 

 presence of a large number of bacteria in a satisfactory 

 and thoroughly washed specimen of sputum indicates 

 that these bacteria probably play an active part in the 



2. The presence of a small number of bacteria in 

 such sputum does not necessarily indicate that they are 

 not active in that case, for they may penetrate more or 

 less deeply into the lung tissue, and produce patho- 

 logical changes without being thrown off in large num- 

 bers with the exudate. It is probable, however, that, 

 as a rule, the smaller the number found the less the 

 degree of mixed infection. 



3. Cases of clinically secondary infection frequently 

 give pure cultures of some one organism which appeared 

 to be capable of causing the symptoms. 



4. In the majority of severe cases of clinically 

 mixed infection many organisms have been found which 

 usually have belonged to several different species or 

 varieties. 



5. In the majority of cases of clinically non-mixed 

 infection very few organisms have been found. 



6. Only bacteria which might cause pathological 

 changes were present. 



7. Very few of the organisms found were virulent 

 in rabbits, even though coming from severe cases of 

 mixed infection. 



The virulence for laboratory animals of bacteria ob- 

 tained from the sputum is, therefore, no indication of 

 their virulence for man, because of the impossibility of 

 reproducing in such animals the exact condition of sus- 

 ceptibility present in human infection. 



General Rules in Microscopical Examination of Sputum. 



