72 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



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 

 modern methods of examination are so useful. 



The finding of tubercle bacilli in the urine is absolute 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 presump- 

 tive 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 

 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 tuberculous one (actinomycosis and glanders, 

 and some other rare diseases, may also give rise to similar 

 negative findings), 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. 200), 

 and (2) the use of Koch's old tuberculin. This is usually con- 

 sidered to be too dangerous for practical use, but if a small 

 dose only be given (TSOO to- ^o 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 vii.) of recently boiled and cooled normal saline solu- 

 tion, containing about J per cent of carbolic acid. Mix well 

 and inject * c.c. (about 3! minims) of the fluid hypodermically. 

 In a positive case there will be a sharp reaction, the tempera- 

 ture rising to 103 or more, and remaining elevated for a day 



