390 TYPHOID FEVER 



allowed to stand for a few hours; a few, loopfuls from the 

 upper part of the tube are spread on a plate of MacConkey's 

 bile-salt lactose agar, and any colourless colonies developing 

 after twenty-four hours' incubation at 37 C. are placed in 

 mannite peptone water. If acid develops there is strong 

 suspicion that the organism is either the typhoid bacillus or 

 dysentery bacilli of the Flexner group (vide infra}. If the 

 organism is motile, causes permanent acidity in litmus milk and 

 acid in glucose, mannite and sorbite but not in saccharose, and 

 if it produces no indol then it usually satisfies an agglutination 

 test with an antityphoid serum and may be definitely accepted 

 as the b. typhosus. For MacConkey's medium the other media 

 described on pp. 47-51 may be substituted. 



Isolation from Water Supplies. A great deal of work has been done 

 on this subject. It is evident that if it is difficult to isolate the bacilli 

 from the stools, it must a fortiori be much more difficult to do so when 

 the latter are enormously diluted by water. The b. typhosus has, how- 

 ever, been isolated from water during epidemics. The b. coli is, as 

 might be expected, the organism most commonly present in such 

 circumstances. In the case of both bacteria, the whole series of culture 

 reactions must be gone through before any particular organism isolated 

 is identified as the one or the other; probably there are saprophytes 

 existing in nature which only differ from them in one or two reactions. 

 In examining waters, the ordinary plate methods are generally used, but 

 the MacConkey or similar media may be employed with advantage. 

 Klein niters a large quantity through a Berkefeld filter, and, brushing 

 off the bacteria retained on the porcelain, makes cultures. A much 

 greater concentration of the bacteria is thus obtained. From time to time 

 various substances have been used with the object of inhibiting the growth 

 of the b. coli without interfering with that of the b. typhosus. Most of 

 these have not stood the test of experience. Lately caffeine has been 

 used for this end. For use in examining waters the following is the 

 method employed : To 900 c.c. of the suspected water there are added 

 10 grms. nutrose dissolved in 80 c.c. of sterile water, and 5 grms. of 

 caffeine dissolved in sterile distilled water, heated to 80 C. and cooled 

 to 55 C. before addition. After mixing the ingredients there is added 

 10 c.c. of '1 per cent, crystal violet. The flask is incubated at 37 C. for 

 twelve hours, and then plates of Conradi-Drigalski medium are inoculated 

 from it. For investigation of fseces, a medium made up as above but with 

 ordinary sterile water may be inoculated and a similar procedure followed. 

 On the whole there is little to be gained from this attempt to isolate the 

 typhoid bacillus from water in any particular case, and it is much more 

 useful for the bacteriologist to bend his energies toward the obtaining 

 of the indirect evidence of contamination of water by sewage, to the 

 nature of which attention has been called in Chapter V. 



THE BACILLUS PARATYPHOSUS AND FOOD-POISONING BACILLI. 



In the b. coli we have an organism having a definite habitat 

 in the animal intestine, and presenting certain cultural characters 



