ISOLATION OF THE COLI-TYPHOID BACILLI 389 



(a) From the Stools. — One or two loopfuls of faeces are emulsified in 10 c.c. 

 bouillon until the medium just begins to be slightly opaque and the tube is 

 allowed to stand until any solid particles have subsided. A loopful from 

 the upper part of the fluid is placed on one or more MacConkey lactose 

 agar plates (or on one of the other similar media) and well spread — the 

 plate being incubated with the medium uppermost. Browning's brilliant- 

 green method (p. 51) may also be recommended. In any case the presence 

 on MacConkey plates of colourless colonies of Gram-negative bacilli con- 

 stitutes presumptive evidence of the existence of pathogenic members 

 of the coli-typhoid group in the faeces. Some of these colonies should now 

 be picked off into bouillon and into mannite tubes. The former are used 

 after a few hours' incubation for investigating motility — the latter for 

 observing fermentation. Growth in mannite without acid or gas points 

 to the presence of the b. dysenteriae, Shiga, if the organism is non-motile, 

 or of Morgan's No. 1 bacillus, if motile ; the development of acid without 

 gas may be due to the b. typhosus, if the bacillus be motile, or to the 

 b. dysenteriae (Flexner or Y) if non-motile ; a culture showing acid and 

 gas associated with motility in the organism indicates one of the para- 

 typhoid bacilli or the b. Gaertner. 1 Agglutination observations may now 

 be made (see infra) and a set of culture tubes appropriate to the organism 

 suspected to be present may be put up ; it is well to include amongst 

 these a gelatine tube, to exclude non-pathogenic varieties, and one of 

 lactose — the latter to be kept under observation for several weeks in case 

 the bacillus be a slow lactose fermenting b. coli. In this connection the 

 fact must always be borne in mind, in dealing with any coli-typhoid 

 bacillus, that its fermentative capacities may be very slowly manifested. 



In any extensive investigation of intestinal infections atypical bacilli 

 will from time to time be encountered which show aberration in the presence 

 or absence of motility, in the formation of indol, in unusual fermentative 

 reactions, etc. ; the significance of these may be difficult to determine. 



The faeces always constitutes an important source of cultures in the 

 diseases under consideration. In typhoid and paratyphoid fevers the 

 causal bacteria may be detected during the incubation period and during 

 the febrile stage, though towards the end of the acute illness the numbers 

 may diminish, and if ulceration is not a marked feature their numbers 

 may not be great at any time. They may persist during convalescence, 

 but gradually disappear in the course of from a few weeks to three months, 

 except in carrier cases. Similar facts obtain in bacillary dysentery. 



(6) From the Blood. — The bacilli of the group may be isolated from the 

 blood by ordinary methods (see p. 70), but a special method is often also 

 used. In this, 5 c.c. of the blood are placed in 10 c.c. sterilised ox bile ; 

 the mixture is incubated for from one to seven days, and from time to 

 time the presence of non-lactose fermenters is tested by inoculating 

 MacConkey plates. In typhoid and paratyphoid infections the organisms 

 have been stated to have been isolated from the blood during the pre- 

 febrile stage and are very usually present while fever exists, especially 

 when the b. paratyphosus is the active agent. In bacillary dysentery 

 a blood infection is not common. It may be said generally that the 

 isolation of an organism of the group from the blood during an acute 

 illness probably furnishes the most significant evidence as to its being the 

 cause of the condition present. 



1 For fuller details consult Henderson Smith, Brit. Med. Journ., 1915, vol. 

 ii. p. 1 : Ledingham and Penfold, ibid, idem., p. 704. 



