58 THE EEPOKT OF THE Xo. 36 



volume, discovery after discovery has been made, until at the present time, practi- 

 cally only a score of years after its inception, the literature on this subject has be- 

 come enormous, the workers in the field constitute an army, comprehensive volumes 

 on medical entomology have been published (two in the United States within the 

 past year), advanced students are taking up the subject as tlieir life work, and 

 as the months go by the field opens further and further until it is evident that its 

 importance especially regarding the etiology of tropical disease, can scarcely be 

 exaggerated. 



So numerous have the discoveries become of late that it would take a course 

 of lectures to display the results, and I must confine myself to-night to compara- 

 tively few, easily illustrated aspects. 



It is convenient, and in fact necessary, to divide the field in any discussion 

 into three categories: 



First, insects as simple carriers of disease, the accidental carriers as it were; 

 that is, insects frequenting places where disease germs are likely to occur, and con- 

 veying these in their stomachs or on their bodies to food supplies. -This class is 

 notably illustrated by the bouse fiy. 



Second, insects as direct inoculators of disease. These are biting insects which 

 feed upon diseased men or animals, and carry the causative organisms on their 

 l)eaks and. insert them into the circulation of healthy individuals. In this way 

 anthrax is carried by biting flies; surra is carried the same way, as is also the 

 nagana or tsetse-fly disease of cattle." So also is bubonic plague carried in this 

 manner by rat fleas, but here there is more than a passive carriage, as is also the 

 case with the tsetse-fly disease. 



The third category, and this is perhaps the most important, insects as 

 essential hosts of pathogenic organisms. These are the cases in which the parasitic 

 organism undergoes its sexual generation in the body of its insect host and another, 

 non-sexual, generation or generations in its warm-blooded host. To this class 

 belong the malarial mosquitoes, the yellow fever mosquito, and the rapidly in- 

 creasing number of species that carry Trypanosomiases, Leishmaniases, Spirocha?- 

 toses, and the ticks that carry relapsing fevers and other fevers of man and 

 animals, and the lice that carry typhus fever. 



Insects as Simple Cakrieks op Disease. 



■ The House-Fly. (Lantern slides and general discussion). 

 Cockroaches, ants and other insects. It is perfectly possible, as above stated, 

 that any insect which comes in contact with, either accidently or for feeding pur- 

 poses, excremental or other material containing pathogenic organisms and tlien 

 passes to the food or bodies of men and animals may thus become a simple carrier 

 of disease. There are plenty of obvious illustrations of this. Darling, in the 

 Canal Zone, has shown that ants which flourish in the tropics may- thus carry 

 disease, and in fact the little house ants in temperate regions may also function 

 in this way. The same thing may be said of cockroaches, and especially of the 

 small so-called German cockroach, which multiplies excessively in unclean estab- 

 lishments, and it may also be said of the latrine fly {Fannia scalaris) which breeds 

 in latrines and which has frequent access to food, although not so greatly attracted 

 to food supplies as is the true house-fly. i\.nd there are numbers of other insects 

 which may from time to time play this part, although, speaking of flies, I pointed 

 out many years ago that over 97 per cent, of the flies found all over the country 

 in dininof-rooms and kitchens, are true house-flies. 



