Other Diseases Transmitted by Insects 163 



extensive skin eruptions occur on all parts of the 

 body and the patient gradually becomes anemic 

 and physically and intellectually feeble. The 

 nervous system seems to be affected by the para- 

 site, either directly or by the action of the toxins 

 it produces. The patient becomes more debili- 

 tated and morose with an increasing tendency 

 to sleep, hence the name sleeping sickness. As 

 the stupor deepens the patient looses all desire 

 or power of exertion and as little food is taken 

 he rapidly wastes away and finally succumbs 

 for after this final stage is reached there is no re- 

 lief. 



It is definitely known that a species of tsetse- 

 fly, Glossina palpalis (Fig. 112), which somewhat 

 resembles our stable-fly, is responsible for the 

 dissemination of the disease, and some recent in- 

 vestigators have suggested that certain species of 

 mosquitoes may also carry the parasite from one 

 host to another. There still remains some doubt 

 as to the exact manner in which the fly transmits 

 the disease, but it seems altogether likely that it is 

 an alternative host and does not serve as a simple 

 mechanical carrier. In this respect it is like the 

 mosquito which is one of the necessary hosts of 

 the malaria parasites, and unlike the house-fly 

 which carries the germs of various diseases in a 



