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THE EFFECTS OF PAEASITES ON THEIR HOSTS. 



The species of Filaria which infest the connective tissue of their 

 host are similar in habit to the itch-mites. They have been usually, 

 but erroneously, regarded as quiescent Entozoa, while in reality they 

 are in constant, though slow, motion. And since many nerves 

 and blood-vessels ramify in this connective tissue, it is on a priori 

 grounds probable that these parasites are the cause of many patho- 

 logical phenomena. 1 These will of course vary widely in detail, 

 according to special conditions, but will especially depend on the 

 nature of the organ attacked and the character of the wandering 

 parasite. Thus Filaria Medinensis moving among the muscles gives 



Fio. 86. — Sarcoptcs scabiei. 



Fig. 87. — Crust of Scalies norvegka, with 

 mites, their borings, eggs, and ex- 

 creta. 



rise usually only to a more or less violent pain, while Filaria loa ^ 

 under the conjunction of the eye causes a chronic inflammation, and 

 Filaria Bancrofti, the parent of the Filaria sanguinis (p. 50), discovered 

 by Lewis, inhabiting the sub- epidermal tissue, especially in the in- 

 guinal region, causes sclerotic and lymphatic changes, which have a 



^ Eisig observed a Filaria in the kangaroo, which had bored through the pericardium, 

 and thereby induced a fatal pericarditis. — Zeitschr.f. wi^s. Zool., p. 99, Bd. xx., 1870. 



^ Through the kindness of Dr. Falkenstein, a member of the German- African ex- 

 pedition, I have had the opportunity of examining a specimen of Filaria loa, and have 

 convinced myself that it is by no means identical with F, Medinensis, but differs widely 

 from that form. The embryos enclosed in thin egg-shells bear a close resemblance to 

 F, sanguinis, but are smaller (0'21 mm.). 



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