FLIES AS CARRIERS OF INFECTION 389 



(4) Aerobic bacillus of malignant oedema (Klein). 



(5) Bacillus lactis aerogenes of Escherich. Found in the intestine 

 of nurslings and in milk. Much like B. coli, but is non-motile. 

 It differs from B. coli by not fermenting dulcitol, by fermenting 

 saccharose and adonit, and by giving the Voges-Proskauer reaction 

 (see Table, p. 381). According to Harden and Walpole, 1 its action 

 on glucose differs from that of B. coli, more alcohol being produced 

 and formed at the expense of that part of the molecule of the sugar 

 which in the B. coli fermentation yields acetic and lactic acids. 



The Voges-Proskauer reaction is obtained by growing the 

 organism in 2 per cent, glucose broth in a fermentation tube (Fig. 17, 

 p. 84) for three days and adding some strong caustic potash solu- 

 tion ; on standing exposed to the air a pink colour develops. 

 According to Harden and Walpole 2 the reaction is probably due 

 to acetylmethyl-carbinol, which in the presence of air and potash 

 is oxidised into diacetyl, which then reacts with some constituent 

 of the peptone in the medium, giving the pink colour. 



The B. lactis aerogenes (which may be classed among the capsu- 

 lated bacilli, see p. 258) is occasionally pathogenic, causing peri- 

 tonitis. 3 In these circumstances, it is capsulated, but the capsule is 

 difficult to stain. It seems probable that the B. capsulatus of 

 Pfeiffer is identical with this organism. 



(6) B. cloacae, (Jordan). Met with in sewage. In general char- 

 acters it much resembles B. coli, but produces more gas (75 per cent.) 

 from glucose and liquefies gelatin in four or five to thirty days. Like 

 B. lactis aerogenes, saccharose is always fermented and the Voges- 

 Proskauer reaction is positive, but neither dulcitol nor adonit is 

 fermented. (See Table, p. 381.) 



Flies as Carriers of Infection 



Flies and other "insects " may convey infection (1) by acting as 

 " porters " and infecting food, etc., (2) by direct inoculation, (3) by 

 inoculation after a cycle of development in which case the carrier 

 is more or less specific ; e.g. anopheline mosquitoes in malaria. In 

 the first method the organisms are generally bacteria, occasionally 

 ova of worms ; in the second, bacteria or protozoa ; in the third, 

 invariably protozoa, filaria, etc., i.e. animal organisms. 



1 Journ of Hygiene, vol. v, 1905, p. 488 ; Proc. Roy. Soc. Lond., B, 

 vol. Ixxvii, 1906, p. 399. 



2 Proc. Roy. Soc. Lond., B, vol. Jxxvii, 1906, p. 399. 



3 See Churchman, Johns Hopkins Hosp. Bull., vol. xxii, 1911, p. 116. 



