74 



NATURE 



[July 21, 1910 



statistics showed tliat water was not a sufficiently 

 important factor in, and was not explanatory of, the 

 typhoid epidemics occurring in certain of the national 

 encampments. Later, in tfie South African war, the 

 same conditions were present, and enteric fever was 

 responsible for a very heavy death-roll ; those who 

 were present directed attention on their return to 

 these conditions, which, as circumstantial evidence, 

 would convince the most sceptical as to the important 

 rdlc that l^ies played in the spread of the disease. 

 These conditions are well known now ; open latrines 

 swarming with incredible numbers of flies in all 

 stages of development ; these latrines frequented by 

 incipient cases of enteric; myriads of flies in the mess 

 tents, defiling all kinds of food, and in many cases 

 distinguishable by the lime which they bore on their 

 appendages from the latrines, as were the typhoid 

 patients in the hospitals also distinguishable by the 

 number of flies clustering about their mouths while 

 in bed. 



From the setaceous character of the appendages 

 and bodies of flies it is only to be expected that when 

 allowed to have access to infected material they would 

 be able to carry the bacilli on their appendages, 

 bodies and in their digestive tracts, and the trans- 

 ference of flies from infected substances to culture 

 media are reallv unimportant experiments compared 

 with those of capturing the flies under normal con- 

 ditions near sources of infection and determining the 

 presence and identity of the micro-organisms on these 

 insects, as certain investigators have done. It would 



X^. 



■^-'*^--,<i>i.-4j^M>Ki^ 



Fig. 2.— Larva of .1/. domatka. 



be found impossible to obtain a specimen of Musca 

 domestica which was not carrying bacteria or fungal 

 spores. 



Though externally they may be almost sterile when 

 they emerge from the pupa, the fly after emergence 

 immediately becomes contaminated, and during the 

 remainder of its varied existence serves as a collector 

 and disseminator of any bacterial or fungal organisms 

 with which it comes into contact. One of the most 

 important and convincing experiments is that of 

 Giissow (hitherto unpublished), who obtained thirtv 

 colonies comprising si.x species of bacteria and six 

 colonies comprising four species of fungi from a 

 single fly caught in the living-room of a house and 

 allowed to walk over a culture plate of agar-agar. 

 From a fly caught in the open he obtained forty-six 

 colonies comprising eight species of bacteria and seven 

 colonies comprising four species of fungi. The tracks 

 of a house-fl)' caught in a household dustbin yielded 

 ii6 colonies of bacteria comprising eleven species, 

 and including such species as B. coli, B. Jactis acidi, 

 and Sarcina ventricuU, and ten colonies comprising 

 six species of fungi. 



Such experimental results render further argument 

 as to the frequency with which house-flies carry bac- 

 teria and the spores of moulds and other fungi un- 

 necessary. Flies captured near e.xcremental products 

 are most frequently found carrying bacteria char- 

 acteristic of the alimentary canal or putrefactive 

 NO. 2125, VOL. 84] 



bacteria, and it is only to be expected that should such 

 sources of contamination be infected with pathogenic 

 bacteria, for example, from an incipient case of 

 typhoid or from a typhoid "carrier," the bodies 

 of the flies would become infected. .As an instance 

 of this, Hamilton recovered B. typhosus five times in 

 eighteen experiments from flies caught in two un- 

 drained privies, on the fences of two yards, on the 

 walls of two houses, and in the room of an enteric 

 fever patient, and others have obtained positive results 

 in similar experiments. 



The habits of these insects are most perfectly suited 

 for the dissemination of pathogenic bacteria. On one 

 hand, thev seek all kinds of excrementous and decay- 

 ing vegetable and other matter, chiefly for the pur- 

 pose of depositing their eggs; and, on the other 

 hand, thev flv with perfect freedom on to food such 

 as milk, sugar, &:c., much of which forms an excel- 

 lent medium for the deposition of whatever bacteria 

 vhev may have be- 

 come contaminated 

 with during their 

 ubiquitous wander- 

 ings. 



Not only durmg 

 the summer, but also 

 during the winter 

 months, house-flies, 

 if they are active, 

 normally carry on 

 their bodies and ap- 

 pendages bacteria 

 and the spores of 

 moulds, and Fig. 3 

 shows an agar slope 

 culture obtained by 

 allowing a fly caught 

 in the 'writer's 

 laboratory at the end 

 of January, 1910, to 

 walk up ' the agar 

 slope ; the compara- 

 tively large number 

 of colonies which 

 developed in the 

 tracks of a single 

 journey can be easily 

 seen. 



The eggs of the 

 house-fly are de- 

 posited on most de- 

 caying vegetable sub- 

 stances, especially if 

 they are in a fer- 

 menting condition ; 

 the influence of fer- 

 mentation is of considerable importance; in one in- 

 stance the maggots developed in germinating wheat. 

 Of all substances they prefer horse manure, and this 

 is most suitable for the development when it occurs in 

 heaps as stable refuse, supplying as it does both 

 moisture and heat, the two great essentials for a 

 rapid development. They will also choose the excre- 

 ments of man and certain other animals. Newstead 

 found them in such animal and vegetable substances 

 as rotting feathers, flocks, and paper, in which sub- 

 stances, when soiled with excrementous matter, they 

 have also been found by the writer, and such condi- 

 tions not infrequently occur in refuse heaps. Wher- 

 ever there are collections of these substances, in such 

 places will flies be found, not only depositing their 

 eggs, but contaminating their appendages and bodies 

 with putrefactive and other micro-organisms which 

 abound there. Ficker and others have shown that 

 typhoid bacilli can pass through the digestive tract 



