338 THE TUBERCLE BACILLUS 



The methods of differentiating the former are considered elsewhere (Chap. 

 XIX.). In the case of the smegma bacillus there is hardly any fear of 

 making a mistake if it be remembered (i) where this organism is found and 

 (ii) that though it resembles the tubercle bacillus in resisting the decolourizing 

 action of mineral acids, it differs from it in being rapidly decolourized by 

 alcohol (probably because alcohol dissolves the fatty matter which impregnates 

 it). In short, if Ziehl-Neelsen's method be carried out in the manner described 

 above no confusion is likely to arise (p. 307). To avoid all possible chance of 

 mistake in difficult cases, Bezan9on and Philibert advise staining in the warm 

 for 10 minutes, decolourizing in 33 per cent, nitric acid for 2 minutes and in 

 absolute alcohol for 5 minutes. 



It must not be forgotten that saprophytic acid-fast bacilli are found in the 

 ambient media, and in milk, butter, etc. (p. 347). 



These organisms might conceivably be a serious source of error in the 

 detection of the tubercle bacillus. But they are often only feebly resistant 

 to acid and are frequently decolourized by absolute alcohol alone. If there 

 be any doubt the difficulty can be cleared up by inoculation. 



Films are prepared in the ordinary way. Tissues should be hardened in 

 alcohol or acid perchloride. [Eastwood (for the English Commission) hardened 

 tissues in 10 per cent, formalin for a few days then washed well in water and 

 transferred to Muller's fluid.] 



2. Inoculations. In those cases, which, in practice, are far from infrequent, 

 in which microscopical examination fails to reveal the presence of the tubercle 

 bacillus resort must be had to animal inoculation. Guinea-pigs being the 

 most susceptible animals are always used for the purpose. When the material 

 is free from other organisms, as, for instance, in the case of caseo-pus, pleural 

 fluid, etc. it may be inoculated into the peritoneal cavity but in other cases 

 (sputum, pus from a fistula, etc.) it is best to inoculate it beneath the skin 

 otherwise there is the risk of setting up a septic peritonitis which will kill the 

 animal before the tubercle bacillus has had time to produce its characteristic 

 lesions. [Our experience would lead us invariably to inoculate intra- 

 peritoneally when the material contains other organisms. It would seem 

 that the peritoneal fluid possesses a quality lacking in the sub-cutaneous 

 tissues of destroying putrefactive and other organisms.] 



For purposes of rapid diagnosis, Nattan-Larrier and Griffon advise the inocula- 

 tion of the suspected material into the mammary gland of a guinea-pig during the 

 period of lactation. The bacilli multiply in the gland and after a week or a fortnight 

 they can be detected in the milk by staining the latter by Ziehl-Neelsen's method. 



Osman Nouri has drawn attention to the advantages of inoculating an animal by 

 rubbing the material into the skin after shaving it (p. 299). 



Bloch advises that the suspected material should be inoculated sub-cutaneously 

 into the inguinal region of a guinea-pig and that the inguinal glands should then be 

 squeezed and manipulated between the fingers to bruise them and so render them 

 more susceptible to infection. Under these conditions, if the material (urine, etc.) 

 contained the tubercle bacillus the glands will be found enlarged, inflamed and even 

 suppurating when the animal is killed 9 days after inoculation. The method is not 

 reliable ; tubercle bacilli cannot be found on microscopical examination when the 

 animal is killed 9 days after inoculation ; moreover under the conditions of the 

 experiment, acid-fast bacilli, Staphylococci, etc. may equally with the tubercle 

 bacillus cause swelling and suppuration of the glands. 



3. Cultures. Cultures are very rarely used as a means of detecting the 

 tubercle bacillus in a pathological product. To obtain cultures not only 

 must the material be rich in tubercle bacilli [and free from contaminating 

 organisms] but there must be a good deal of it. Cultures, however, are 

 particularly successful in the case of sputum. 



