78 BACTERIOLOGICAL DIAGNOSIS. 



the sputum of a person who had presented no sym- 

 ptoms of the disease for eight years and was apparently 

 cured. But a person in whom the bacilli are present is 

 always in danger of a recrudescence of the disease, and 

 may be a soiirce of infection. Absence of the bacilli does 

 not disprove the diagnosis of tuberculosis ; bacilli do 

 not appear in the sputum until the lung-tissue in which 

 they occur breaks down, and are therefore absent in the 

 early stages of acute tuberculosis. 



In some cases of ordinary chronic phthisis bacilli may 

 occur in the sputum in very scanty numbers and may be 

 missed unless a very careful search is made. Bacilli 

 should not be considered as being absent until well 

 stained films have been examined for at least half an 

 hour, and the examination repeated on several occa- 

 sions. 



The finding of tubercle bacilli in the urine is prac- 

 tically absolute proof of tuberculosis of some part of 

 the urinary tract, probably the kidneys or bladder. 

 Absence of bacilli implies nothing unless the exam- 

 ination has been made very thoroughly and repeated 

 several times at intervals. Then it affords presumptive 

 evidence that the urinary passages are free from the 

 disease. 



The same is true of the examination of pus. Tubercle 

 bacilli rarely occur in inflammatory exudates except in 

 very small numbers and can only be demonstrated by 

 animal experiments. If you examine pus from a 

 chronic abscess and find no organisms of any kind it is 

 almost certain that the process is a tubercular one ; and 

 the negative evidence obtained by the failure to find 

 tubercle bacilli should not be allowed to carry much 

 weight. The same is true for the clear exudates. 



