66 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



considered as possibly carried by insects. Of course there is a 

 limit to the possibilities and other modes of infection must be 

 well considered. This leads us to mention a danger that con- 

 fronts us, namely, a possible tendency to exaggerate the impor- 

 tance of insect transmission and overlook, even in cases where 

 insects may be occasionally concerned, the greater importance 

 of other modes of infection. The function of air, water, food and 

 contact will always be important and the enthusiast would do 

 well to weigh them deliberately. The danger of drawing con- 

 clusions is shown by the recent history of pellagra. Doctor 

 Sambon evolved a theory of insect transmission which fitted very 

 well into the known facts in the epidemiology of the disease. 

 He found its geography, seasonal incidence, and other features 

 to be explained by transmission by Simulium reptans. Its causa- 

 tive organism could not be found and was therefore probably 

 protozoan and ultra-microscopic like that of yellow fever which 

 is insect-borne. It occurs commonly in persons living near run- 

 ning water. Therefore its possible vector was an aquatic insect. 

 It breaks out in the spring which suggests an insect most preva- 

 lent at that season. Simulium is a biting insect which lives in 

 rapidly running water and is most abundant in the spring. There- 

 fore Simulium was the transmitter. Many interesting details in 

 this theory will be recalled by those who have had the pleasure 

 of hearing the impressive statements of Doctor Sambon. Further 

 work, however, shows the presence of pellagra in regions where 

 Simulium does not occur and the whole theory appears to have 

 been based upon a series of coincidences. 



As a matter of fact there will always be considerable danger in 

 conclusions based upon epidemiological findings. To find that 

 the range of some insect coincides with the range of a disease 

 especially if the insect meets other requirements is suggestive of 

 some form of some important relation to the malady, but trans- 

 mission experiments are quite necessary to prove it. It is obvious 

 that the danger is greater in the case of diseases in which the 

 causal organism is unknown. Where the organism is known the 

 finding of it in the insect under suspicion is a simple and effective 

 guard against error. 



All of the foregoing is preliminary to some observations on 

 urgent needs of the present which entomologists should hasten 

 to fill. The whole study of insect-borne and possibly insect- 

 borne diseases is hampered by a lack of sufficient knowledge of 

 the insects involved. To illustrate, at one point in the work of 

 the Thompson Pellagra Commission certain observations seemed 

 to show that the head louse might be the vector. It would possi- 

 bly explain the striking difference in incidence by sex better than 

 any other insect. Exact knowledge about the abundance, habits, 



