TUBERCULOSIS. 265 



perature, or from one or two hours at 37 .(98.6 F.) in the 

 thermostat. They are decolorized in ten per cent, nitric acid 

 for about two minutes until they appear greenish blue, then in 

 seventy per cent, alcohol until they appear pale rose. Next, 

 they are introduced into water, counterstained with a dilute 

 aqueous solution of methylene-blue or vesuvin for two or three 

 minutes, dehydrated in absolute alcohol, cleared in cedar-oil, 

 and mounted in Canada balsam. 



(/) Examination of Milk for Tubercle-bacilli. The milk is 

 advantageously first centrifugated. Before being stained the 

 cover-slip preparations are placed for from four to six minutes 

 in chloroform for extraction of the fat. On their removal the 

 chloroform is permitted to evaporate. 



Fig. 58. Tubercle-bacilli in the urine; from a case of tuberculous cystitis (Jakob). 



The demonstration of tubercle-bacilli in the sputum ren- 

 ders unequivocally certain the diagnosis of pulmonary 

 tuberculosis. A negative result permits of a definite con- 

 clusion only when frequently repeated. The demonstration 

 of tubercle-bacilli in the stools permits of a diagnosis of 

 intestinal tuberculosis only in the absence of primary pul- 

 monary tuberculosis. If this is present, it may be con- 

 cluded that sputa have been swallowed, the bacilli of 

 which appear in the feces unchanged. For this reason 

 examination of the stools but rarely yields practical results. 

 If urinary sediment is stained from a suspicion of genito- 

 urinary tuberculosis, the possibility of confusion with 

 smegma-bacilli (see Syphilis) must be considered, as these 

 bacteria also, when exposed to acids, retain tenaciously the 



