SCIENCE AND INDUSTRY. 
The Relation of Insects to the 
Dissemination of Diseases. 
By EWEN MACKINNON, B.A., B.Sc. 
The subject of entomology in its relation to the transmission of» 
diseases by insects, or, as we might call it, the entomology of disease, 
has been placed on a firm footing by the investigations carried ont 
during the great war. By the co-operation of entomologists, para- 
sitologists, doctors, chemists, sanatarians, engineers, and others, many? 
problems affecting the health of large armies have been satisfactorily 
solved. Everything had to be handled on an enormous scale; materials 
and methods had to be standardized and made available for millions. 
Such problems as the control of the louse, the bug, the fly, and the 
mosquito haye led to the introduction of numerous types of latrines, 
incinerators, sterilizers, steam disinfectors, and oil distributors. The 
subject of insect repellants was studied very thoroughly, and’ many 
new chemicals were made and tested. Probably the greatest advances 
were made with the investigations on the louse and bug problems, and 
resulted in proving that such diseases as typhus, relapsing and .trench 
fevers, were transmitted by the louse and the bed bug, but not by 
biting, as has been almost universally assumed. The infection is caused 
by the louse or bug being scratched into the flesh, or by haying their 
feces scratched in. -They breed in filth, and are to be controlled by 
cleanliness, heat, water, and chemicals. This involved the sterilization 
of all clothing, and the bathing of whole armies. Steam ster?lization 
‘experiments led to investigations on the shrinking of woollens, the 
bactericidal effect of each process in the laundry; also the effectiveness 
of very many chemicals as insecticides, and as impregnating substances, 
the duration of effectiveness and the effects on skin and clothing. The 
results achieved with the louse and bug have given indications of why 
many experiments in the past on the transmission of disease: by insects 
have failed. It is of interest, therefore, to consider the ways in which 
insects transmit disease. The principles are very much the same in 
plant or animal pathology, and the technique is similar. In fact, in 
‘the relation of bacteria to plant diseases, the whole of the procedure 
has developed from animal pathology, and Koch’s rules for the proof 
of the parasitism of an organism are followed by the plant pathologist. 
An important point to remember is that the healthy plant cell and 
the plant sap, like the human blood, are all in their normal condition 
free from living organisms. Pasteur was the first to show this when 
he proved by culture experiments that grape juice taken from. the 
interior of sound berries was free from micro-organisms. Chamber- 
land also, in 1880, working in Pasteur’s laboratory, showed that beans 
taken directly from the interior of their pods were free from bacteria. 
Tt was Burrill (U.S.A., 1878-1883) and Wakker (Netherlands, 1883) 
who first proved satisfactorily by cultures and inoculations that bac- 
teria cause plant diseases. Burrill determined the cause of pear blight 
to be a bacillus which is now known as Bacillus amylovorus, and Wakker 
652 
