July 21, 1910] 



NATURE 



75 



of the house-fly and retain their virulence for more 

 tlian three weeUs, but the more recent discovery bv 

 l-'aichne. that flies bred from larvae which have 

 developed in infected material carr\' the typhoid bacilli 

 in their digestive tracts, is one of great importance 

 in its practical bearing. 



The most important factor which affects the 

 numbers, activity, and potential danger of flies is 

 temperature. Experiments show that at a high tem- 

 perature the whole life-history can be passed in eight 

 days. Further, it was found that the second genera- 

 lion of flies are able to begin to deposit their eggs as 

 early as the fourteenth day after emerging from the 

 pupa ; in short, the second generation of eggs mav 

 be deposited in about three weeks after the deposition 

 of the first. Each fly is able to deposit from loo to 

 150 eggs in a single batch, and at least six batches 

 are laid during the lifetime of a single female. It is 

 not difficult, in view of these facts, to understand the 

 production of enormous numbers of flies during hot 

 weather, and how the activity and numerical abund- 

 ance of flies increases with the rise of temperature. 

 During the hot months of July, .August, and Septem- 

 ber flies are most abundant, and it is a significant 

 fact that in those years when the temperature is high 

 during those months, that is, during the third quarter 

 of the year, there is almost invariably a high mor- 

 tality from typhoid fever and the infantile disease, 

 summer diarrhoea. In connection with summer or 

 infantile diarrhoea, a curve prepared from statistics 

 covering the last twenty years showed, with the excep- 

 tion of one year, that a rise or fall in the number of 

 deaths per thousand living in a large English city was 

 associated with a rise or fall respectively in the tem- 

 perature. 



The relation of flies to summer diarrhoea is prac- 

 tically based on epidemiological and other circum- 

 stantial evidence, since the specific cause of the 

 disease has not yet been determined with certainty. 

 Morgan, however, has found a bacillus occurring in 

 a large percentage of the cases of the disease, and 

 the same bacillus has been isolated from flies captured 

 in infectea houses. An objection has been made to 

 the idea that the house-fly is a carrier of the cause 

 of summer diarrhoea, this objection being founded 

 on the fact that at the end of the summer the fall in 

 the fly curve follows the fall of the curve representing 

 the diarrhoea mortality, the flies being still more 

 numerous than they were earlier in the season, when 

 the diarrhoea curve was rising. In meeting such an 

 objection it mav be pointed out that we are not con- 

 sidering the numerical abundance of the flies in the 

 houses only; it should be remembered that with a 

 decline of temperature the activity of the flies, 

 especially out of doors, which is important in this 

 case, is not so great, even though their numbers may 

 be considerable indoors. With the fall of the tem- 

 perature, therefore, the possibility of their carrying 

 •the infection decreases without a necessarily corre- 

 sponding decrease in their numbers, and the diarrhoea 

 curve will fall in consequence. 



The flv problem, which is more serious in the 

 United States and Canada than in England, is one 

 that may be attacked and solved in cities and towns, 

 provided that the authorities will take the necessary 

 steps. .As in districts previously infested with mos- 

 quitoes, these insects have been reduced to a negligible 

 quantity bv the abolition of their breeding-places or 

 the rendering of the same unsuitable for the larvae; 

 so also the number of flies and their danger could be 

 lessened very considerably by the removal of their 

 breeding places, by preventing their access to the 

 breeding places, or by treating these with substances 

 noxious to the larvae or flies. Flies are a public 

 nuisance, and, therefore, to maintain places where 

 NO. 2125, VOL. 84] 



flies are able to breed should be made a mis- 

 demeanour. Stable refuse should not be left exposed 

 for a longer period than six or seven days in the 

 summer, but should be removed from the 

 vicinity of dwellings or treated with such a 

 substance as chloride of lime, which will prevent the 

 breeding of the flies, the refuse being kept in a closed 

 fly-proof chamber. The presence of mews and stables 

 with their exposed rubbish heaps will always account 

 for the abundance of flies. The household dustbin or 

 other repository for kitchen refuse, unless securely 

 closed or screened and regularly emptied, also form's 

 an excellent breeding ground. Public tips on to 

 which all kinds of organic and decaying matter is 

 deposited produce their flies in myriads; it is in- 

 variably found, where actual investigation has been 

 made, that the percentage of cases of zymotic diseases 

 of an enteric nature is abnormally high in the neigh- 

 bourhood of public refuse tips and depots where 

 rubbish is allowed to accumulate. 



In considering the relation of house-flies to disease, 

 although the one species of fly, Musca domestica. 

 usually constitutes from 90 to 98 per cent, of the fly 

 population of houses, certain other species are also 

 found to occur. The lesser house-fly, Homalomyia 

 canicidaris, has the next place in the scale of frequency, 

 and is generally mistaken by the uninitiated for a 

 young house-fly, on account of its general re- 

 semblance. Although both the adult fly and the larva 

 have pronounced structural differences, the habits of 

 the larva and the economic relationships of the fly 

 resemble those of M. domestica. The blood-sucking 

 fly, Stomoxys calcitrans, is not infrequently mistaken 

 for the true house-fly, which has adopted vicious 

 habits. M. domestica, however, is unable to pierce 

 the most delicate skin, and S. calcitraus, which 

 frequently enters and is found in houses in the spring 

 and also in the autumn, especially in rural houses, 

 presents considerable differences, the chief being the 

 possession of an awl-like, piercing proboscis, a more 

 robust build, and its coloration. Not infrequently 

 inflammatory swellings, sometimes of a serious 

 nature, result from the "bite of a fly," and such 

 cases are instances of the mechanical transference of 

 such bacteria as the Streptococci from infected 

 material to a healthy human being by a blood-sucking 

 fly. Malignant pustule may be caused by the 

 mechanical transference of the Bacillus anthracis by 

 a blood-sucking fly, or it may be bv a non-blood-suck- 

 ing fly, such as the blowfly, Calliphora erythrocephala, 

 if the skin is broken to provide entrance for the bacillus. 



Wherever there is filth, suppuration, or purulent 

 discharge, flies are invariably attracted, and as they 

 are cosmopolitan in their attentions and no distin- 

 guishers of persons, they are potential disseminators 

 of such bacteria as these substances may contain. 

 It is not a question of eradication in the case of this 

 insect; such is impossible. Control and prevention, 

 however, are within the bounds of possibility, and 

 these will be regarded as essential when the facts are 

 more generally realised. C. Gordon Hewitt. 



THE NEXT TOTAL ECLIPSE OF THE SUN. 



ON April 28 of next year there will occur a total 

 eclipse of the sun which will begin on the earth 

 generally at 7h. 49'2m. G.M.T., the central phase 

 commencing at 8h. 46'im. G.M.T. The path of the 

 moon's shadow is restricted for the most part to the 

 equatorial regions, and is confined to the longitudes 

 between Australia and South .-Xmerica, so that as far 

 as Europe or .Asia are concerned the eclipse cannot be 

 observed there even in a partial phase. 



The actual line of central eclipse commences on 



