44 WATER 



the tubes or colonies reacting are each subcultivated into litmus- 

 milk, glucose litmus broth (in a double tube), and lactose-peptone 

 solution (in a double tube). 



All the organisms giving cultural characters in these media 

 which accord with those of B. typkosus are then fully worked out. 

 The tests should include accurate and extended agglutination 

 tests with highly dilute sera. 



Some such procedure as the above will rapidly decide whether 

 any typhoid bacilli have been isolated. 



Examination for Spirillum cJiolerae. 



Of the different methods suggested, the simplest and most 

 satisfactory is the enrichment method employed by Koch and 

 others. This is best done by converting the water itself into a 

 nutrient medium by the addition of peptone and salt. 



About a litre of the water is placed in twelve large sterile 

 flasks, 90 c.c. in each. To each is added 10 c.c. of a sterile 

 solution, consisting of 10 per cent, peptone, and 5 per cent, 

 sodium chloride. The flasks are then incubated at 37 C. An 

 alternative plan is to use only one flask containing I litre of 

 the water and to add the peptone salt solution to this. Even 

 quantities of ten litres can be treated in this way or, if incu- 

 bators of sufficient size are not available, the water can be dealt 

 with in a series of smaller bottles (2 to 4 litre capacity). After 

 six, twelve and eighteen hours' incubation, microscopic prepara- 

 tions and examinations in hanging drop are made from the 

 surface of each flask. The medium is one in which the cholera 

 spirillum grows very rapidly, and if present, is found in the very 

 thin pellicle on the surface of the liquid. 



According to Koch, after six hours' incubation is the most 

 favourable time to examine but sometimes it is necessary to 

 wait longer. The flasks which show the presence of vibrios are 

 used to inoculate plates of the media selected, a loopful of the 

 fluid being withdrawn from the surface for this purpose. 



When large quantities of water are examined some of the 

 concentration methods described as suitable for the isolation of 

 the typhoid bacillus may be used. 



