THE TUBERCLE BACILLUS. 327 



acids, it is readily decolored by absolute alcohol. The 

 smeg"ma bacilli of diverse origin show unequal resistance 

 to decoloration with acids. It is not transferable to ani- 

 mals and is very difficult to cultivate. The animal experi 

 ment will again demonstrate the tubercle bacillus. The 

 smegma bacillus should be expected, whenever urine or 

 secretions of the genito-urinary apparatus are examined. 

 The same or a similar organism has apparently been found 

 in the mouth, and in lung gangrene. 



To differentiate from the tubercle bacillus the specimen which 

 has been stained with carbolic fuchsin should be decolored by immer- 

 sion for some minutes in a saturated absolute alcoholic solution of 

 methylene blue; or by an acid alcoholic solution (alcohol 97, HCl 3) for 

 10 minutes. Another procedure is to treat it with absolute alcohol 

 for at least three hours, then with five per cent, chromic acid for at 

 least 15 minutes, after which it is stained with carbolic fuchsin, de- 

 colored by exposure to dilute sulphuric acid for 2-3 minutes, and 

 finally stained with concentrated methylene blue. 



In order to cultivate the smegma bacillus it is advisable to ino- 

 culate a tube of liquefied agar, cooled to 50°, with the suspected ma- 

 terial. By means of a sterile syringe about 2 c.c. of blood should be 

 drawn from the vein in the arm (see Chapter XIV), and this is then 

 mixed with the agar. The blood agar mixture is poured into a 

 sterile Petri dish, which is then set aside for a day or two at 37°. 

 The colonies should be examined for bacilli which resist decolor- 

 ation by acids. 



3. — From milk, butter, timothy hay, cow-dung, etc., 

 bacteria have been isolated which stain like the tuber- 

 cle bacillus, and have indeed been mistaken for this 

 organism. Guinea-pigs, as a rule, survive injection 

 whereas rabbits appear to be immune. The inoculated 

 guinea-pigs may die in a month or two. Numerous small 

 nodules or tubercles are present in the mesentery, peri- 

 toneum, liver, lungs, etc. Cultures made from these tuber- 

 cles develop in three or four days and apparently atten- 

 uate rapidly. The tubercles do not show giant cells, or 

 caseation. It is evident, therefore, that in some instances 

 it is necessary to supplement the cover-glass examination 

 by a histological study of the suspected tubercles. Bacteria 



