166 Arthropods as Direct Inoculators of Disease Germs 
the tsetse-flies are not to be found. It is thought to be spread by 
various species of blood-sucking flies belonging to the genera Stomoxys, 
Hcematobia, and Tabanus. Mitzmain (1913) demonstrated that in 
the Philippines it is conveyed mechanically by Tabanus striatus. 
The sleeping sickness of man, in Africa, has also been supposed 
to be directly inoculated by one, or several, species of tsetse-flies. 
It is now known that the fly may convey the disease for a short 
time after feeding, but that there is then a latent period of from 
fourteen to twenty-one days, after which it again becomes infectious. 
This indicates that in the meantime the parasite has been under¬ 
going some phase of its life-cycle and that the fly serves as an inter¬ 
mediate host. We shall therefore consider it more fully under that 
grouping. 
These are a few of the cases of direct inoculation which may be 
cited as of the simpler type. We shall next consider the rdle of the 
flea in the dissemination of the bubonic plague, an illustration 
complicated by the fact that the bacillus multiples within the insect 
and may be indirectly inoculated. 
The Role of Fleas in the Transmission of the Plague 
The plague is a specific infectious disease caused by Bacillus pestis. 
It occurs in several forms, of which the bubonic and the pneumonic 
are the most common. According to Wyman, 80 per cent of the 
human cases are of the bubonic type. It is a disease which, under 
the name of oriental plague, the pest, or the black death, has ravaged 
almost from time immemorial the countries of Africa, Asia, and 
Europe. The record of its ravages are almost beyond belief. In 542 
A. D. it caused in one day ten thousand deaths in Constantinople. 
In the 14th century it was introduced from the East and prevailed 
throughout Armenia, Asia Minor, Egypt and Northern Africa and 
Europe. Hecker estimates that one-fourth of the population of 
Europe, or twenty-five million persons, died in the epidemic of that 
century. From then until the 17th century it was almost constantly 
present in Europe, the great plague of London, in 1665 killing 68,596 
out of a population of 460,000. Such an epidemic would mean for 
New York City a proportionate loss of over 600,000 in a single year. 
It is little wonder that in the face of such an appalling disaster sus¬ 
picion and credulity were rife and the wildest demoralization ensued. 
During the 14th century the Jews were regarded as responsible 
for the disease, through poisoning wells, and were subjected to the 
