PATHOGENIC BACTERIA. 103 



Milk. They grow very well in milk without producing any 

 visible changes in its composition. 



Carbolized-Gelatine. Gelatine which has added to it j^ per 

 cent, carbolic acid will allow the typhoid bacillus to develop, 

 other similar bacilli being destroyed. 



Staining. Colored with the ordinary aniline dyes, when they 

 are warmed ; since they are easily decolorized, acids should be 

 avoided. 



Grain's method is not applicable. Tissue sections stained as 

 follows : 



Alkaline blue 1 hour. 



Alcohol 5 seconds. 



Aniline oil 5 minutes. 



Turpentine oil 1 minute. 



Xylol and Canada bals. 



Such a specimen should first be examined with low power, to 

 focus little colored masses, then examined with immersion lens ; 

 these masses will be found composed of bacilli. 



Similar Bacteria. The Neapolitanus bacillus of Emmerich or 

 faces bacillus of Brieger resembles the typhoid bacillus in many 

 ways, the colonies being the same and its structure similar. 

 But the growth on potato is very different ; a thick, } 7 ellow, 

 pasty layer is formed thereon. 



In Water. Bacilli have been found which also resemble 

 typhoid bacilli, and one must be very careful to make any 

 positive statement. 



Examination of Water for Typhoid Bacilli. When a water is 

 supposed to contain typhoid bacilli, 500 c.cm. of the same is 

 mixed with 20 gtts. of ^-per cent, carbolic acid, which destroys 

 many of the saprophytes. 



Plates are then made as described under Water Analysis. 



Those colonies which then form and have a tendency to liquefy, 

 are touched on second day with permanganate of potassium, 

 and when so colored, destroyed with bichloride of mercury. 



Those that now develop are transferred by inoculation to fresh 

 plates. At the end of eight days they are examined under 

 microscope ; every colony not possessing motile bacilli is dis- 

 carded. The motile bacilli are tested with Gram's method of 



