406 ISOLATION OF THE TYPHOID BACILLUS 



5. Incubate the latter for 15 or 20 hours then plate a few drops from each 

 tube on litmus-lactose-agar. At the same time sow sub-cultures in ordinary 

 broth for inoculation later. 



6. The plates are to be examined and the colonies tested as described 

 above. 



With this method Besson has succeeded in isolating the colon bacillus, 

 the typhoid bacillus, and Friedlander's bacillus from water. 



3. Methods based on precipitation. 



When a chemical precipitate is produced in a liquid containing micro-organisms, 

 a large proportion of the latter are carried down mechanically with the precipitate, 

 so that if the latter be collected the organisms originally present in the liquid are 

 concentrated in a small volume. The principle here involved is the basis of several 

 methods for the detection of the colon and typhoid bacilli in water. Their only 

 advantage is in the concentration of the micro-organisms, since the nature of the 

 organisms and the presence of the typhoid bacillus can only be definitely established 

 by carrying out a series of experiments on ordinary lines using the precipitate as the 

 original material. 



A. Vallet's method. Pour 20 c.c. of the water under examination into a sterile 

 tube, add 4 drops of a saturated aqueous solution of hyposulphite of sodium and 4 

 drops of a saturated solution of lead nitrate. A precipitate forms which carries 

 down with it the majority of the organisms present in the water (the chemicals used 

 have no bactericidal action on the typhoid bacillus). Centrifuge the mixture and 

 suspend the deposit in a few drops of the hyposulphite solution. Sow the liquid 

 which now contains all the organisms originally present in the 20 c.c. of water on 

 Eisner's gelatin (vide ante). 



B. Schueder's method. In Schueder's method the fluid is not centrifuged. Pour 

 2 litres of the water under examination into a tall vessel and add 20 c.c. of a 7*75 per 

 cent, solution of hyposulphite of soda and 20 c.c. of a 10 per cent, solution of lead 

 nitrate. Mix intimately and allow to stand for 20 hours. Decant the supernatant 

 liquid and suspend the precipitate in 14 c.c. of a saturated solution of hyposulphite. 

 Sow the emulsion in quantities of 0'5 c.c. on a number of litmus-lactose-agar 

 plates. 



C. Picker's method. Ficker precipitates the organisms with sulphate of iron. 

 To 2 litres of the suspected water add 8 c.c. of a 10 per cent, solution of soda and 

 7 c.c. of a 10 per cent, solution of sulphate of iron. The precipitation takes 2 or 3 

 hours to complete. Centrifuge the precipitate and dissolve the deposit in one- half 

 its volume of a 25 per cent, solution of neutral tartrate of potassium. Sow the 

 solution on Conradi and Drigalski's medium by the dilution method (p. 407). 



D. Miiller's method. The precipitation is effected by means of oxychloride of 

 iron which acts more quickly than the sulphate and does not require that the water 

 shall be made alkaline. 



To 3 Litres of the water under examination add 5 c.c. of the oxychloride solution. 

 Precipitation is complete in about half an hour. Collect the precipitate on a filter 

 and sow, without re-dissolving, either on Conradi-Drigalski plates or, better (Meter), 

 on malachite-green-agar plates (p. 409). 



4. Method based on the motility of the typhoid bacillus. 



Gambler, in examining water for the presence of typhoid bacillus, relies upon the 

 property possessed by the organism of rapidly passing through porous membranes 

 (p. 155). 



Place a porous porcelain bougie in a large test-tube. Half fill both the bougie 

 and the tube with ordinary broth, and sterilize in the autoclave. Sow the suspected 

 water in the lumen of the bougie and incubate at 37 C. As soon as the broth in the 

 test-tube becomes cloudy sow a little of it on any of the ordinary media used for 

 differentiating the typhoid bacillus. 



This method is not very reliable since some strains of the colon bacillus also pass 



