484 APPENDIX 



is a positive result with the 50 per cent., 5 per cent., and 0*5 per cent., 

 the case is undoubtedly one of typhoid fever, and if in half-an-hour there 

 is no reaction in all three, the result is definitely negative. Intervening 

 degrees of reaction must each be judged on its own merits, and a 

 subsequent examination made. 



From the compilation of a large number of cases, the New York 

 Health Board concludes that Widal's reaction is present in typhoid 

 fever : — 



From the fourth to seventh day in 70 per cent, of the cases. 



From the eighth to fourteenth day in 80 per cent, of the cases. 



During the third and fourth weeks in 90 per cent of the cases. 



It is absent throughout in 5 to 10 per cent, of the cases. 



Widal's reaction persists in the blood for months, or even years, but 

 after three or four months is usually feeble. 



Differentiation of B. Typhosus 



On p. 48 will be found some of the chief distinguishing tests for the 

 typhoid bacillus, which produces no gas in any media, does not coagu- 

 late milk, and stains by Gram's method. McConkey's test for B. coli 

 may also be used. The medium which he makes use of is bile-salt- 

 lactose agar, which is prepared as follows : To 1000 c.c. of tap- water in 

 a flask are added 2 per cent, of peptone, 0'5 per cent, of sodium tauro- 

 cholate, and 1*5 per cent, of agar. The flask is autoclaved at 105° to 

 110° C. for one and a half hours. The mixture is then cooled, mixed 

 with white of egg, and filtered ; then 1 per cent, of lactose is added. 

 The medium is distributed into test-tubes, 10 c.c. in each, which 

 are sterilised by steaming for 15-20 minutes on each of three successive 

 days. Plates are made and incubated at 42° C. for forty-eight hours. 

 There is a marked difference between the colonies of the organisms of 

 the typhoid group and those of the colon group. Of the typhoid group 

 the surface colonies are small, round, raised, and semi-transparent, the 

 deep one lens-shaped, white, and opaque, the medium remaining clear. 

 Of the colon group the surface colonies are roundish or irregular, with 

 flattened tops, opaque, white, with a yellow or orange spot in the centre ; 

 a few have a haze round them. "The deep colonies all have a haze 

 round them, and are lens-shaped and orange-white. The haze is due 

 to precipitation of the sodium taurocholate by acid produced by fermen- 

 tation of the lactose. McConkey and Hill * have further modified this 

 method by the use of a bile-salt broth, composed as follows : Sodium 

 taurocholate, 0*5 per cent. ; glucose, 0"5 per cent. ; peptone, 2 per cent. ; 

 water, 100 c.c. The constituents are dissolved by heat, and the mixture 

 is filtered. After filtration, sufficient neutral litmus is added to give a 

 distinct colour, and the medium is then distributed into Durham's fer- 

 mentation tubes. These, are ordinary test-tubes containing a piece of 

 light-glass tubing, about an inch in length, closed at the upper end. 



* Thompson Yates Laboratories Report, 1901, vol. iv., part i., p. 151, 



