INTRODUCTION 21 



As already noticed, Glossina and Cordylobia, though they 

 are not specially modified for intimate and permanent con- 

 tact with their host, must be reckoned as parasites positive. 



B. ARTHROPOD "CARRIERS" THAT AFFECT MAN. 



(a) Accidental and Casual Carriers : Miastors. 



Here, first of all, should be placed flies, like the common 

 house-fly, which in ways that are mainly mechanical (see 

 p. 32) may spread abroad any kind of hardy pathogenic 

 germs, but are not fixed and necessary agents for the 

 distribution of the germs of any particular species. 



Any kind of predatory Arthropod that habitually attacks 

 man is a potential carrier of this sort, as also is any omnivor- 

 ous domestic insect (cockroach, ant, etc.) that may pollute 

 provisions. 



Carriers of this kind maybe called Miastors (imida-T(iop = 

 a carrier of pollution). 



(b) Qualified or Adapted Carriers. 



An adapted carrier — commonly known as an " interme- 

 diate host " — is a species, parasitic or not, that serves, at the 

 very least, as a specific vessel for carrying a specific parasite 

 on a definite course between two specific points. Among 

 such carriers we meet with several shades of definition : — 



(i) Carriers like Cyclops (p. 313), in which the embryo of 

 the specific parasite, as it swims free in water, is cribbed, 

 cabined, and confined. If the Cyclops with its inside passenger 

 be swallowed by the right species (Man), the Cyclops is 

 digested and the passenger thus liberated to follow its 

 destination as a parasite of the human host. 



(ii) Carriers like certain species of Culex, Stegomyia, 

 Mansonia, Anopheles, Phlebotomus, and Glossina; perhaps 

 also Cimex and Conorhinus ; that in satisfying their thirst 

 for blood imbibe a specific blood-parasite from one victim, 

 and after a definite period (during which the parasite takes 

 advantage of the opportunity to be fruitful and multiply) 

 inject it into the blood of another victim of the same suscept- 

 ible species. 



(iii) Carriers like some Glossina;, that may take a specific 



