64 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



crudescence of the disease, and may be a source 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 

 occasions. It is in these cases that the carbolic method of 

 examination is so useful. 



The finding of tubercle bacilli in the urine is practically abso- 

 lute proof of tuberculosis of some part of the urinary tract, 

 probably the kidneys or bladder. Absence of bacilli implies 

 nothing unless the examination has been made very thoroughly 

 and repeated several times at intervals. Then it affords pre- 

 sumptive 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 often only be demonstrated by animal experi- 

 ments. If you examine pus from a chronic abscess and find no 

 organisms of any kind, it is almost certain that the process is a 

 tuberculous 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. 



In suspected cases of tuberculosis, in which no infective 

 material is forthcoming, there are two methods which may be 

 used : (i) The estimation of the opsonic index (see p. 148), and 

 (2) the use of Koch's old tuberculin. This is usually considered to 

 be too dangerous for practical use, but if a small dose only be given 

 (Tffff c.c), and if it is not employed on cases in which there is a 

 mixed infection, I believe the danger to be practically nil. The 

 tuberculin is sold in i-c.c. bottles. For use, add the contents of 

 one of these to 200 c.c. (about gvii.) of recently boiled and cooled 

 normal saline solution. Mix well and inject i c.c. (rn xvii.) of 

 the fluid hypodermically. In a positive case there will be a sharp 

 reaction, the temperature rising to 103° or more, and remaining 

 elevated for a day or so. 



Information may also be obtained in some cases by a blood- 



