BACILLUS ICTEROIDES. 



457 



have some causal relationship to the disease. Sanarelli, in 1897, obtained 

 cultures of an organism which he named bacillus icteroides, and which he 

 considers to be the cause of yellow fever. It is not identical 

 with the "bacillus x," the latter being a variety of B. coli. 



This organism has rounded ends, is 2-4 /A long, about 

 .5 fj. broad, often occurring in pairs (Fig. 155), staining by 

 the ordinary stains but decolorising by Gram's method. It 

 is motile and possesses four to eight flagella. It grows on all 

 the usual media ; on gelatin plates after twenty-four hours the 

 colonies are minute points somewhat transparent to the naked 

 eye, and under a low power have a finely granular appearance. 

 After six or seven days there appears somewhere in the colony 

 a focus of more active growth, forming an opaque centre, from 

 which granular striae radiate to the periphery. The gelatin is 

 not liquefied. The most characteristic growth is that on sloped 

 agar. After twenty-fours at 37 C. there is a grey iridescent 

 and somewhat transparent growth. On being transferred to 

 a temperature of 20 C. to 28 C. this becomes in twelve 

 hours surrounded by a halo of white, opaque, pearly growth 

 of higher .level than the central part. In a few days the 

 growth at the lower temperature becomes liquid in character 

 and runs slowly down the medium as a drop of melted 

 paraffin would do (Fig. 156). Growth also takes place in 

 bouillon and blood serum. On potatoes there is a fine trans- 

 parent pellicle which does not alter its colour with age. Lit- 

 mus milk is rendered faintly acid, the cream-ring turning 

 gradually blue, and after a lapse of several days the acid 

 reaction of the medium gives place slowly to an alkaline 

 change; no coagulation occurs. The bacillus ferments glu- 

 cose, but not lactose or saccharose. It occasionally gives a 

 feeble indol reaction. 



Sanarelli investigated twelve cases of yellow fever and 

 found the B. icteroides present in relatively small numbers 

 in six. It appeared chiefly in the capillaries of the liver and 

 kidneys, rarely in other parts of the body. It was never found 

 in the gastro-intestinal tract. 



Inoculation experiments did not give characteristic re- 

 sults, but Sanarelli states that sterile bouillon cultures, when 

 injected subcutaneously or intravenously in man, give rise to all the symptoms 

 of yellow fever. 



According to Sanarelli 7 s view the bacillus is to be looked on as settling 

 chiefly in the liver and kidneys and there producing very powerful toxins 

 whose chief effects are on the cells of these organs and on the small blood- 

 vessels of the body, thus causing the rupture of vessel walls which frequently 

 results, and opening up a path for infection by other organisms which may 

 produce secondary infections. Sanarelli states that the serum of yellow-fever 

 patients clumps the B. icteroides in a dilution of i : 40. The reaction is said 

 to appear on the second day. 



FIG. 156. 

 Culture of Ba- 

 cillus icteroides 

 on agar, show- 

 ing the charac- 

 teristic appear- 

 ance when 

 incubated at 

 the two tem- 

 peratures men- 

 tioned (Sana- 

 relli). Natural 

 size. 



