68 
feet and body of the fly, and in this way might be carried to 
food on which the fly subsequently settled. That this was 
actually the case was shown by the exhibition of a photograph 
of a culture-plate upon which a fly had crawled. The tracks 
of its feet were indicated by colonies of baccilli which had 
subsequently grown there. In this way fever had been 
conveyed in Cuba, and in Egypt an eye disease was carried 
by the fly. Flies are largely responsible for the spread 
of infantile diarrhoea. Observations made in Manchester 
by Dr. Niven in 1905 showed that the increase in the number 
of flies preceded by about three or four days an increase in 
the number of fatal cases of infantile diarrhoea ; consequently 
it was imperative, especially where infantile mortality was so 
serious a question as in Burnley and other Lancashire towns, 
to diminish the number of flies by every possible means. 
Horse manure should be promptly gathered and kept covered 
so that flies may not have access to it, and as a further pre- 
caution a surface dressing of chloride of lime was desirable. 
Flies should be excluded from houses, and especially from 
contact with food. The use of sticky fly-catchers and fly- 
traps in houses during hot weather, was to be recommended 
also. Flies were not nearly so abundant or dangerous in this 
country as in hotter countries, but still they were sufficiently 
so to warrant them in excluding them from their houses 
and especially from contact with their food. 
Stegomyia, a relative of the common gnat, had been 
proved to be the carrier of yellow fever. Its life history was 
similar to that of the gnat. They abound in the West Indies, 
South and Central America, in parts of Africa and Australia, 
and recently he had seen specimens from Spain. As it sucked 
the blood of a person suffering from this fever some of the 
fever-germs were taken into the gnat’s body, where they 
evidently underwent changes. After an interval of twelve 
days, the fly was capable of transmitting the disease : on 
taking its next meal of blood from another person it injected 
some of the fever-germs into his blood. It was curious that 
in spite of the researches of many eminent workers on this 
subject, the germ of yellow-fever, which must be excessively 
minute, had not yet been discovered. We know that it is 
so minute that it passes through the pores of unglazed porce- 
lain. 
The mosquito (anopheles) too had its machinery for biting 
and it was the blood-sucking habit of the female mosquito 
(the males do not suck blood but feed on plant juices) which 
was responsible for the spread of malaria. The apparatus 
for blood sucking, when not in use, was carefully bestowed 
