68 
Insects AS Factors IN THE SPREAD OF BacTERIAL DISEASES. 
By SEVERANCE BURRAGE. 
From the earliest times theories have been advanced relative to the 
spread of disease by insects. Just what part the insect played of course 
was unknown, and naturally must have remained unknown until the 
discovery of bacteria and their relations to diseases firmly established. 
But since the germ theory has been established the subject of insects and 
disease has received much attention, although not all that it may have 
deserved. The bibliography on the subject, collected by Dr. George H. 
F. Nuttall, numbers nearly four hundred papers and articles, many of 
them representing exhaustive experimental work, and others are of gen- 
eral interest, and of practical value. 
Books on hygiene and sanitary science, even the latest editions, do not 
mention insects as disease-spreading factors, yet they go into detailed 
discussions of many less important subjects. Undoubtedly many epi- 
demics of contagious and infectious diseases have been caused directly 
or indirectly by insects, and then laid at the door of the water supply, 
infected food, or bad drainage. While water or milk may have been the 
immediate means of spreading the disease among large numbers of indi- 
viduals, one insect may have caused the infection of the water or the milk. 
As a disease carrier, we must regard an insect in one of two classes. - 
He may be either the simple carrier of the bacteria, transporting the 
germs of disease on or in his body from an infected person to some healthy 
person’s environment, the bacteria being wiped off from the insect’s body 
or deposited in his excreta on the food or clothing of the susceptible 
healthy person; or the insect may be an intermediate host, in which the 
parasite or germ undergoes a part of its life cycle, and then the germ is 
transmitted to the healthy individual through the sting of the insect, 
the insect’s fang acting as the inoculating needle. 
In the latter class the mosquito and cattle tick are the best known, 
the mosquito carrying the malarial plasmodium, and the tick the organism 
of Texan cattle fever. Notwithstanding the importance of these diseases 
from the hygienic standpoint, they do not come under the head of bacterial 
diseases, as they are caused by animal parasites. It would, perhaps, be 
well to mention, however, in passing, that the theory connecting mosqui- 
