188 BACTERIOLOGICAL EX A MI NATION OF WATER. 



When broth was used, the medium was inoculated with the 

 typhoid bacillus and kept at 36 C. until a good growth was 

 obtained. The chemical substance was then added, and the 

 culture kept at the room temperature for four or five hours. At 

 the end of this time, and ten to fifteen hours later, half a cubic 

 centimetre was plated out in a " roll culture." The results 

 obtained by Kitasato are given in the table on page 187. 



Kitasato's results with carbolic acid do not agree with my 

 observations. The percentage of caustic lime required to kill the 

 typhoid bacillus is also much greater than that given by other 

 observers. Liborius found that 0'0074 per cent, of caustic lime 

 destroyed the typhoid bacillus when growing in broth. Kitasato 

 explains the discrepancy by the fact that he used concentrated 

 broth, whereas Liborius employed broth diluted fifteen times, 

 with distilled w r ater. The phosphates present in the undiluted 

 broth required to be neutralised by the lime before this substance 

 could act on the bacilli. By using a diluted broth, Kitasato. 

 found that 0'0074 per cent, of lime destroyed the typhoid bacilli. 



MICRO-ORGANISMS WHICH RESEMBLE THE B. TYPHOSUS. 



There are many organisms which may be mistaken for the 

 B. typhosus unless great care is taken to apply the tests already 

 mentioned. In polluted waters B. coli and its varieties occur,, 

 and, before the modern tests were elaborated, there is no doubt 

 that this great group of micro-organisms was often confused 

 with the B. typhosus. There is, however, at the present day 

 not much difficulty in separating the great bulk of these- 

 organisms from the typhoid bacillus. The following table gives, 

 the reactions of the typical B. typhosus and B. coli : 



B. COLI COMMUNIS. B. TYPHOSUS. 



(1) Surface Colonies, Gelatine Plates. (1) Much thinner than those of 

 Thicker, and grow more rapidly B. coli, and grow more slowly. After- 

 than those of B. typhosus. After forty-eight hours incubation at 22 C,. 

 forty-eight hours incubation at 22 C. they are hardly visible to the naked 

 they are usually large and character- eye. 



istic. 



(2) Gelati tie-stab. Quick growth (2) Slow growth on the surface like- 

 on the surface and along the line of the colonies ; along the line of inocu- 

 inoculation. lation the growth is much thinner, and 



often ends below in a few white points, 

 consisting of discrete colonies. 



