314 BACTERIA PATHOGENIC TO MAN 



sumably of exudate from the deeper portions of the lungs, are so great 

 that the collection of the specimens should be supervised by the bacteri- 

 ologist in charge of the work of examination. 



2. Specimens of sputum collected even with the greatest precaution 

 may give evidence of decided mouth infection unless immediately 

 washed. 



3. The sputum must be examined very soon after collection. 



4. The culture medium used for the final cultures must be suitable 

 for the growth of the micro-organisms. 



5. At least two successive examinations of sputum should be made 

 in each case. 



6. The results, especially as to the number of colonies, vary accord- 

 ing to the size and tenacity of the ball of sputum washed e. g., a small 

 ball of sputum which becomes more or less broken up upon thorough 

 shaking may contain very few or no bacteria. 



Williams, in the examination of the sputum in some 40 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 disease. 



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 

 pathological changes without being thrown off in large numbers 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 cul- 

 tures of some one organism, which appear 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 very virulent in rabbits, 

 even though coming from severe cases of mixed infection. 



The virulence for laboratory animals of bacteria obtained 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 susceptibility present in human infection. 



General Rules in Microscopic Examination of Sputum. Always make 

 two still preparations from each specimen. Report no result as 

 negative until at least two preparations have been subjected to a 

 thorough search with a 1/12 oil-immersion or 2 mm. apochromatic lens 

 by means of a mechanical stage. From a very large experience in 

 the examination of sputum for tubercle bacilli, the New York Health 

 Department bacteriologists have concluded that the examination of 



