May 13, 1915 | 
NATURE 
291 

“Flies undoubtedly served as carriers of infec- 
tion.” 
An estimate of the fly population and its relation 
‘to admissions for enteric fever was made by 
Ainsworth in Poona, where enteric has a very 
‘definite season. A definite number of fly traps 
was set, and the daily catch taken as a measure 
‘of the fly population. The observations showed 
that the abundance of flies increased earlier than 
the admissions for enteric, and, speaking gener- 
ally, the rise in fly population ante-dated the rise 
in enteric cases by about one month. 
Taking into account the incubation period for 
the disease, this fact is in agreement with the 
view of a causal relation between cases and flies 
in Poona. 
In considering the possible influence of flies in 
the spread of typhoid in a well-sewered city, it 
must be remembered that the opportunities for 
them to pick up the infection are 
vastly fewer than under the condi- 
tions of a military encampment, 
or even in rural surroundings. 
In large cities with modern 
sewerage, dejecta and urine from 
patients may be left available to 
flies, but the bulk goes promptly 
into the main drain, and similar 
observations to those above-men- 
tioned have shown no close rela- 
tionship, in point of time, 
between cases of typhoid and 
prevalence of flies in London, 
‘Washington, cr Manchester. 
As with typhoid, the case 
against flies as agents in the dis- 
tribution of the infection of 
cholera is circumstantial, as other 
means of spread cannot be ex- 
cluded. Take, for instance, the 
case of an accumulation of 1 
300,000 pilgrims in Puri, India, 
in July, 1912, which was studied 
by Greig. The sanitary accom- 
modation of the town was inade- 
quate for such an accession to 
the population. Some of the 
pilgrims imported the infection of cholera, and 
an outbreak occurred. Flies in Puri “amounted 
almost to a plague,” and a bacteriological 
examination of the legs and the contents of the 
alimentary tracts of flies caught in the neighbour- 
hood of cholera cases demonstrated the presence 
of cholera vibrios. 
Knowing the habits of flies, it is impossible to 
forgo the conclusion, arrived at by Greig, that 
some amount of distribution of the infection of 
cholera was due to their activity. But to what 
extent they were contributing could only be 
ascertained by the result of measures directed 
either to the diminution of their numbers, or to 
depriving them of access to infectious material. 
_ Greig could not supervise the private latrines 
of the native inhabitants, but was able to carry 
out practical measures to prevent flies from: visit- 
NO. 2376, VOL. 95] 
dated 10 Cays 


13 June20 27 July4 14 

ing dejecta in the case of an outbreak of cholera 
amongst a limited population in the Puri jail. 
These were attended with immediate good results. 
There are the same general reasons for 
assuming that fly transmission plays an important 
part in epidemics of summer diarrhoea of infants 
as in the case of typhoid and cholera. Anyone 
familiar with the domestic ménage of the average 
working man on a hot summer day, with the 
baby sick with diarrhoea, and other small children 
to care for, must realise that the opportunities 
afforded for flies to transport the infective agent 
from the dejecta of one child to the food supply 
of another are more than adequate. 
Epidemic diarrhcea of children does not occur 
except during that season of the year when flies 
are abundant and active, and, as will be seen 
from the accompanying chart, the relation be- 
tween fly population and diarrhoea cases is so 
' 
1 
’ 
v 
18 25 Augi 8 15 22 29 SeppS 12 19 26 Oct3 10 47 2% 34 
Fic. 3.—Dr. Hamer’s observations on relation in point of time between prevalence of flies and diarrhea 
mortality in London, 1908. 
(x41 fly-collecting centres.) The deaths from diarrhoea have been ante- 
striking as to suggest something more than a 
mere accidental dependence upon the same 
phenomena. 
The chart is constructed from Dr. Hamer’s 
observations on the numbers of flies caught daily 
in the same number of traps in 141 localities in 
London during 1908. An important point brought 
out by these observations is the dependence of 
both the number of flies and the epidemic upon 
the cumulative effect of previous warm weather 
—as, for instance, is indicated by the earth tem- 
perature four feet below the surface, a fact to 
which attention was directed by Ballard in 1889. 
Similar observations in Manchester, by Dr. Niven, 
in 1904 to 1906, showed the same relationship. 
The reason why the number of flies should be 
dependent upon this factor is obviously that 
the generation time (cycle from egg to egg) is 
