68 



THK 



PROTOZOA AS PARASITES OF MAN 



The invertebrates responsible for the spreading of Trypanosoma 

 gamhunse are the tsetse flies. Glossina palfalis and G. tachinotdes 

 (Fig 40) These are similar in size and general habits to the 

 clegs of the English countryside. They suck the blood of various 

 backboned animals-cattle, antelopes, birds, reptiles, and so 

 forth as well as man— and thus take into their stomachs such 

 parasites as ma>' infest the blood vessels of its victims. When the 

 object of the attack of Glossina is infected with the trypanosome 

 of sleeping sickness, the insect becomes capable of inoculating 

 a new host in the course of its feeding. The power is soon lost, but 

 is regained after about twenty days. It seems probable that the 

 first inoculations are made with trypanosomes which are still 



Fig. 40. — The tsetse fly Glossina palpalis. — From Thomson. 



fresh in the proboscis of the insect, but the later ones with 

 individuals which arise from the stumpy forms after passing 

 through a course of development in the insect's alimentary 

 canal and salivary glands. During this development the stumpy 

 forms become first long and slender, then, attached to the wall 

 of the salivary gland, they pass through a ' crithidial phase ' in 

 which the membrane starts in front of the nucleus ; finally, as 

 stout-bodied, mature individuals, they are injected with the 

 saliva when a new victim is bitten. 



Besides gambiense there are known a number of other trypano- 

 somes : T. rhodesiense which causes a sleeping sickness in the 

 southern part of Central Africa, and is transmitted by G. morsitans, 

 G. swynnertoni and G. pallidipes ; T. brucei, the cause of a disease 

 of horses and cattle in South Africa ; T. equinum which causes a 



