676 BACTERIUM 



Mention should perhaps be made here of an organism that appears to be responsible for 

 joint ill of foals, and that is referred to by a variety of names, such as B. nephritidis equi, 

 B. equirulis. Bad. viscosum equi, and B. pyosepticus equi. Morphologically, this organism 

 is a pleomorphic Gram-negative bacUlus occurring singly, in streptococcus-like chains, and 

 as filaments. Some authors describe it as capsulated, others as non-capsulated. It forms 

 tenacious colonies on agar, gives rise to a very viscous sediment in broth, gives a nail-head 

 growth in gelatin stab without Uquefaction, ferments glucose, maltose, mannitol, lactose, 

 and sucrose with the production of acid but not gas, is M.R. — , V.P. — , citrate — , indole — , 

 reduces nitrates to nitrites, produces acid, and sometimes clot, in Utmus milk, is antigenic- 

 ally heterogeneous, and is non-pathogenic to laboratory animals. The normal form on 

 isolation is said to be mucoid, but a non-mucoid variant is sometimes cultivated directly 

 from foals, though more often it is seen only as the result of in vitro variation. (For refer- 

 ences see Edwards 1931, 1932.) The exact relationship of this organism to the members 

 of the Friedlander group is doubtful. 



A detailed description of Friedlander's bacillus is given on p. 680. 



The Paracolon Group 



There remain a number of organisms which, for one reason or another, cannot 

 be included in any of the lactose-fermenting groups already described, or in either 

 of the non-lactose-fermenting groups to be considered in the next two chapters. 

 These organisms ferment lactose late, weakly, irregularly, or not at all. Some 

 constantly give rise to non-lactose-fermenting variants. Some produce gas 

 abundantly, and some in only small quantity ; others are completely anaerogenic. 

 A few species are pathogenic for man ; others are under suspicion ; and others 

 again are almost certainly non-pathogenic. Some are found in faeces, some in 

 water, some in soil, and some in other situations. 



This heterogeneous collection of organisms we propose to refer to as paracolon 

 bacilli. They constitute a group that appears to be intermediate between the 

 coliform bacilli on the one hand and the non-lactose-fermenting Salmonella and 

 Shigella bacilli on the other. From the coliform bacilli they are distinguished 

 mainly by their late fermentation of lactose, or by their failure to ferment it at 

 all. From Salmonella and Shigella they differ mainly in fermenting either lactose, 

 sucrose, or salicin and in their lack of the particular antigens that characterize 

 these two groups. 



Paracolon bacLlU have frequently been isolated from the faeces of persons suflFering 

 from enteric-hke infections, enteritis and cystitis. Occasionally an organism belonging 

 to this group has been isolated from the blood stream. In very many instances, however, 

 they have been cultivated from the faeces of normal persons (see Sandiford 1935) ; and 

 it seems doubtful whether they have any real significance as primary infecting agents 

 in epidemic infections of the enteric or dysenteric type, though there can be no doubt 

 that some species at least possess pathogenic potentiahties when they invade the tissues 

 from the intestinal tract. The great majority of the organisms included in this group 

 have, it may be noted, been isolated in the tropics ; and there seems no doubt (Sandiford 

 1935) that they are a more common constituent of the normal intestinal flora under 

 tropical than under temperate conditions. 



The classification of these strains raises problems of considerable difficulty. Various 

 schemes have been suggested (Chalmers and Macdonald 1916, Castellani and Chalmers 

 1920, Castellani 1938) ; but these are not m accordance with the general hnes that we 

 have discussed above, and in the authors' opinion lay too much stress on minor differences 

 in fermentative abUity. Stuart, Wheeler, Rustigian and Zimmerman (1943), who have 

 subjected several members of this group to the series of tests used for differentiating 



