PROC. ENT. SOC. WASH., VOL. 20 NO. f>, MAY, Hils 93 



may assume that such requirements are almost necessary to suc- 

 cessful investigation of disease-transmitting insects. There are 

 other phases of the subject, however, which do not require such 

 intimate knowledge of microorganisms. These are the study of 

 the ectoparasites of man and animals, and also of those insects 

 which from some cause or other become endo-parasites. 



Sanitary entomology is really the putting into effect of a knowl- 

 edge of the life history of the insects which cause and carry disease. 

 Entomological sanitation involves many features of engineering 

 but is by no means an exclusively engineering problem. 



Thus it will be seen that medical entomology is a necessary part 

 in the great chain of subjects relating to the health of man and 

 animals. It is a link, which, if absent, prevents a correct inter- 

 pretation of protective medicine. We are all aware of the part 

 health has in winning this war. It is obvious therefore that medi- 

 cal entomology must have a vital part in the great conflict. I 

 shall attempt in a cursory manner to show some of the phases of 

 entomology's part. 



THE BIOLOGICAL PHASE OF THE SUBJECT. 



We have not been in the habit of looking on medical subjects 

 often enough from the purely biological side of the question. Not 

 many generations ago the medical profession would have denied 

 any biological problems outside the subject of the disease itself. 

 Now we know that for every disease there is a cause, and usually 

 this cause is directly or indirectly an organism. 



Types of Relationships. 



The science has now progressed far enough so that we are be- 

 ginning to recognize certain types of interrelationships between 

 the disease organism and its host. Possibly we may make a 

 tentative grouping as follows: 



Type 1. The simple relationship existing purely between a 

 given vertebrate species and a given organism, with the trans- 

 mission voluntary or involuntary, but direct from individual to 

 individual. Simple insect parasitism may be classed here, as for 

 instance bots, lice, mites, confined to single hosts. 



Type 2. Such a simple relationship but with the possibility 

 of a third species carrying the organism on its body, or in its body, 

 without altering it or enabling it to multiply or continue its devel- 

 opment. Insects have been convicted in numerous cases of such 

 a mechanical transmission of disease, as for instance the trans- 

 mission of Trypanosoma hippicum, the cause of murrinaof mules in 

 Panama from infected lesion touninfected injury by the housefly, 

 Musca domestica; and also the transmission of anthrax by the 



