102 INSECTS ANE DISEASE 
lymphatics, enter the blood stream, where they may be 
discovered in the blood of the superficial vessels during 
evening or night, as minute lively motile worms, dis- 
appearing in the daytime. Culex fatigans is a nocturnal 
insect, and bites during the hours when the filarie are near 
the surface. Sir Patrick Manson, many years ago, dis- 
covered that the embryo filarie escape from the stomach 
of the mosquito and develop in its thoracic muscles, in- 
creasing largely in size. This discovery has been confirmed 
by many later observers, among whom I may name Dr. 
Thomas Bancroft. More recently it has been shown that 
the larvae, when sufficiently grown, penetrate from the 
thorax of the mosquito into the proboscis, and from thence 
enter the blood stream of the human subject during the 
act of biting. 
MOSQUITOS AND MALARIA. 
Since the earliest beginnings of medical science it has 
been known that the inhabitants of certain districts, and 
visitors to those districts, are peculiarly liable to attacks 
of fever, characterised by their intermittent or remittent 
course. To these many different names have been given, 
such as ague, splenic fever, intermittent or remittent fever, 
paludism, malaria, besides a large number of local names 
derived from the districts in which fevers are prevalent. 
Though largely confused with other fevers, they had certain 
peculiarities, such as a frequent tendency for the attacks 
to recur at daily intervals, or on alternate days, or every 
third day, the so-called quotidian, tertian, and quartan 
agues. As a rule these attacks recurred at the same hour 
of the day, and often ran through three stages, more or 
less defined, the cold, hot, and sweating stages. It was 
also well-known that those who had suffered from such 
attacks were very apt to suffer from them again, even after 
long intervals of time, and removal to healthy districts, 
where the disease was not known to occur. Again, those 
who had suffered much from these attacks were known to 
develop an enlargement of the spleen, and, when micros- 
copical examination became a method of research, deposits 
of minute particles of a blackish pigment were found in 
the spleen and other organs after death. In the seventeenth 
